Forests and Climates in the South Island of New Zealand.
[Read before Wellington Branch. February 17, 1954, received by the Editor, February 19, 1954.]
In Part 1 of this report on the indigenous forests of the South Island of New Zealand, an analysis is made of the many striking peculiarities of forest species and forest type distribution and behaviour evident in the forests of Western Southland. These peculiarities are shown to be explicable in terms of an hypothesis stating, briefly, that the forests, as a whole. are in an unstable condition consequent on comparatively recent changes in regional climates; and that, as a result, an active le-distribution of species is in progress with resultant development of a wide range of new, though by no means stable, forest types,
In Part II of the report. the forests of eastern and inland regions of the South Island, forests region now generally possessing semi-arid grassland climates, are examined and are shown to demand formulation of the same hypothesis for adequate explanation of their distribution and condition; and this hypothesis is shown not to be in conflict with evidence derived through studies of the soils or through study of Polynesian traditions.
In Part III. the salient features of forest type distribution and behaviour for certain other South Island forest regions are outlined in demonstration of the fact that the forests of these legions are also comprehensible in terms of the hypothesis.
In Part IV it is shown that the phenomena discussed in preceding sections of the report are b [ unclear: ] o means peculiar to New Zealand forests but that, nevertheless, there are valid reasons for the prominence of these features in New Zealand forests in comparison With the forest, of other countries And, in Part IV, also, implications inherent in the hypothesis are briefly discussed.
|Part 1.—The Forests Of Western Southland|
|The Alton Reversals||334|
|The Rowallan Reversals||340|
|The Mid-slope podocarps of the Longwood Range||343|
|Biotre Barriers Geological Accidents and Seed Sources||346|
|The Coastal Terrace Podocarps||351|
|Matai. an Important Climatic Indicator Species||353|
|Part II—The. Matai Cforests, Past and Presen T.|
|The Warau Valley Matai Forests||355|
|The Ancient Warau Valley Forest||360|
|The Matai Forests of Canterbury and Otago||364|
|The Forests of Banks Peninsula, Mt. Peel and the Upper Rakaia||367|
|The Destruction of the Forests||372|
|Part III.—Further Notes On The Forests Of The South Island|
|The Beech Forests of Eastern and Inland Districts||375|
|The Westland Rimu Forests||379|
|The South Westland Beech/Podocarp Forests||383|
|The Beech/Podocarp Forests of North Westland and Western Nelson||387|
|The Beech Forests of Inland Nelson||393|
|The Forests of Eastern Marlborough||396|
|The Forests of Frordland||398|
|Part IV.—General Discussion Of The Facts And Hypotheses.|
|Concerning the Prominence of Mal-adjustment Features in South Island Forests||402|
|Some Implications and Research Requirements||406|
|References to Literature||408|
|Table of Plant Names Employed||410|
No matter for what particular purpose a forest is to be managed, for timber production, for the protection of the soil, for the control of waters, for the maintenance of aesthetic, scientific or recreational values, or for multiple use, success in management is contingent upon possession of a thorough understanding of the whole forest. Management, to be successful, must be founded in a deep appreciation of the forest, of its origins and structure and of the complex interrelationships of all its component parts. And, since a forest is an ever-changing, living community, management also demands unremitting study of all trends in forest evolution, man-made or natural. For any single forest the complex actions and interactions of plants, soils, animals, micro-organisms and men, together with all factors of climate, topography, lithology and history, must be studied separately and in synthesis.
The prosecution of such studies is no simple or short term task; and a full understanding is unlikely to be gained by any individual student however competent. In this field of endeavour it is almost impossible to isolate a single, sharply defined problem from the tangled mass of inter-related problems producing, by diligent research, a polished memoir unassailable in fact and in logic. We must be satisfied if, aiming at the stars of final truth and complete comprehension, we can present what appears to be one aspect of the truth for consideration and evaluation by our critics and fellow students.
In these circumstances it is very easy to succumb to the temptation of delaying publication of our few facts and many hypotheses in the forlorn hope that the investigations in hand might be brought to completion; but such perfection is unattainable and perfectionism in a science where experiments require many lifetimes for completion is strongly to be deprecated. It could serve only to delay progress by placing impediments in the path of successful team work or by focussing undue attention upon the trivia of methodology. Method is important but, in the study of ecology, methodology can become a fetish dressed up in ponderous verbiage but divorced from reality and sterile of significant results.
This then, constitutes the justification and, in part, the apology, for presentation of this interim report on incomplete work Fundamentally the report is little more than a formulation of the working hypotheses elaborated during the course of a primary field survey, hypotheses which may serve to open up fresh lines of attack on outstanding problems. In default of such a primary survey, research objectives remain obscure with frequent and gross mis-direction of effort. The first requirement is always the search for the mental tools, the working hypotheses, which can later be used to delimit and define specific problems for more intensive investigation But. it must be stressed, the hypotheses themselves are not facts though they may sometime be proven to be substantially founded on fact. This note of caution must be sustained throughout the reading
of this report. It may be that some alternate hypotheses will better explain the facts; this report will have served its purpose if either the present hypotheses are substantiated or alternately, if it leads to the formulation of better ones.
Primary survey in heavily forested, frequently mountainous country is both arduous and time consuming. In the depths of the forest mental and physical energies must largely be expended on the immediate problems of load-carrying, track-cutting, direction-finding and so on, with but little time left for more ethereal matters. But to work only in those portions of the forest which are readily accessible generally leads to the investigation of edge effects but not to study of the real forest; and to work in the forest only on fine warm summer days reveals nothing of those many things which can be learnt during the bleak wet winter months. Very largely, however, our present knowledge of the forests stems from such summer day, forest margin reconnaissances. This has been unavoidable. Trained workers have been few and part-time. Therefore, without decrying the efforts of the past, the paucity of our present knowledge is understandable, and the frequency of errors and omissions is excusable. Even yet, it is essential to point out, the task of primary survey is incomplete.
With the development of modern methods of aerial photography, however, a new tool of great research value has been placed in our hands. Through its use the physical labour can be reduced and the tempo of the work speeded up. In particular, many things can now be seen clearly which before were obscure. Each forest can now be seen as a single organic unit and the relationships of all its major component parts are clearly discernible, a substantial advance on the old composite picture built up of casual glimpses and imperfect descriptions obtained along a line of march. By means of this new technique many forests have now been re-surveyed and re-examined in considerable detail and the work actively continues. (Thomson, A. P., 1947 and 1949; Holloway, 1949). Understandably, many matters and many points of detail have come to light which are at variance with the old imperfect descriptions; and in many instances these new facts are irreconcilable with the old hypotheses covering the nature and distribution of the forests. New hypotheses have been required to fit the new facts.
A complete exposition of the subject would undoubtedly demand a preliminary recapitulation of the facts as known at the commencement of the present surveys but this could not be done within the scope of this report. Reference should be made to Cockayne's monumental treatise (Cockayne, 1928). Since publication of this work no major advance in the study of the forests has been made though a little descriptive material has been added. Cockayne's work still forms the basis of ecological studies as taught in the schools and universities. He was a leader in what might, to-day. be called the classical school of plant ecologists. He expounded the basic theory of the subject, the doctrines of plant association and succession, the theory of the climatic climax, and, by adopting a broad geographical approach, he was able to reconcile the facts as then known with the hypotheses then held. But, it must be emphasised, the approach was very broad and the framework of fact was tenuous in the extreme. Few of Cockayne's hypotheses, though representing substantial improvements on ideas previously current, have led to any real advance in the field of practical forest management. Basically, the principal error would appear to have lain in his adoption of too static an outlook. He distinguished and described a multiplicity of forest types
some, admittedly, being regarded as relatively unstable and destined to eventual replacement by types nearer to the ‘climatic climax’; but the changes visualised proceeded infinitely slowly over immense periods of time measurable, in certain instances at least, on a geological time scale. For all practical purposes, Cockayne's forest types were stable types developed in accordance with a pattern set by present climates.
Cockayne did not make use of an hypothesis of ancient climatic instability in explanation of the phenological and morphological peculiarities so evident in many New Zealand plants and also in broad explanations of the over-all distribution of podocarp, beech and kauri forests; but, again, the time intervals were immense. The possibility of relatively short term climatic variation was not seriously considered. Climates were generally considered sufficiently stable to permit full development of climax forms of vegetation.
Speight (1910) in explanation of the forest remnants once to be found throughout the eastern grasslands was compelled to assume comparatively recent changes in climate; but the argument was never carried through to its logical conclusion, namely, that the changes could have been so recent that existing forests bear the imprint of the old climates to this date, that existing forests are in a plastic and unstable condition, and that, in forest types and species distribution, existing forests are largely out of phase with respect to present climates.
This is the crux of the new working hypothesis. The classical theories of plant association and succession tending toward the ultimate development of climatic climax associations are accepted, but any attempt to describe any existing forest types as climax associations is rejected. The new hypothesis states that the present forests are in a state of disequilibrium with rapid changes still in progress consequent on comparatively recent climatic disturbances. It follows that such a thing as a stable type of forest may be, in this country, unknown. A few types of forest may have achieved a position of near stability but in general, New Zealand foresters concerned with management of the indigenous forests deal with a peculiarly complex agglomeration of relict types of forest and with a host of new types in which the processes of adjustment and re-adjustment to the new climates are in active progress.
The unravelling of this complex, assuming the hypothesis to be really founded on fact, is a matter of very considerable moment. We can no longer assume that the species that grew in the old forests (and still survive therein to-day) can be re-grown in those forests in the future. The sites on which certain species attained their optimum development in the past might not be the sites on which they could most successfully be managed to-day. Optimum utilisation of the land resource might demand the planned replacement of an old species by a new one better adapted to the site conditions of the present. And so on. The possibilities are legion; and the hypothesis, if substantiated, must influence the future management not only of the forests but. directly or indirectly, of the whole land resource. The forests, the native grasslands and the soils will inevitably bear the same stigmata of change.
This has already been recognised with respect to the soils of one region (Raeside. 1948) With respect to the grasslands the signs might not prove so evident since these grasslands have been subjected to a greater measure of cultural interference than have the forests But the evidence should still be there.
Again, if there have been comparatively recent changes in New Zealand climates, the matter should prove of no small import in other fields of scientific enquiry, to the anthropologists, zoologists and glaciologists to name but a few. The possibilities have been argued by workers in these fields though inconclusively. But it does not lie within the scope of this report to cover these related grounds. Nor does it lie within the scope of this report to review the immense volume of overseas work on the general subject of historical climatology. Reference should be made to the standard texts (Huntington, 1941; Zeuner, 1946; Brooks, 1949). Present hypotheses were formulated solely on evidence derived through study of the forests and the text will be restricted thereto, in so far as is possible, holding references to other work to the barest minimum.
At the same time, to the maximum extent possible, the technical phraseology of the professional ecologist has been avoided so that the report might be read with greater mental comfort by workers in related fields: and the “popular” names of plant species (wherever such names are in common use) have been employed, a full glossary of plant names being appended To a certain extent, therefore, apologies might be offered to such ecologists as read the report and feel it desirable to re-translate into the appropriate jargon. To them, also, the term ‘forest type’ as used herein should be explained as being a simple forester's term denoting any clearly distinct unit of forest vegetation. It covers. and is applied to, any vegetation unit irrespective of its ecological status from a prisere to a climatic climax association. And the term ‘stand,’ wherever used, is to be considered as roughly synonymous with the term ‘forest type.’
Finally, a word might be said in explanation of the decision to restrict the subject matter of this report to the forests of the South Island, eschewing reference to the forests of the North Island. Comparable phenomena to those detailed in this report for southern forests are traceable in the northern forests but the over all position in the north is of greater complexity than is the position in the south. In the northern forests a greater number of forest tree species are involved than are encountered in the south, with resultant major difficulties in interpretation of the patterns of forest re-adjustment, and. at the same time, the patterns of change are not so pronounced in the north since, apparently, the climatic changes experienced, though possibly of equal magnitude in the two islands, were not operative over so critical a range in the north. Furthermore, the patterns of change over wide areas in central regions of the North Island are confused and concealed in a maze of ‘re-adjustment patterns’ stemming, not from climatic variations, but from extensive volcanic cataclysms. By and large, the clues to an understanding of the North Island forests are to be sought in study of the simpler forests of the South Island. These latter must first be understood. The northern forests can later be interpreted in terms of southern discoveries.
The Forests Of Western Southland
The first, forests to be re-surveyed in the South Island were those of the Western Southland region. Work commenced (1946) in the forests of the Longwood Range and it soon became apparent that they could not be satisfactorily type-mapped for management purposes employing criteria of stand differentiation based on ecological theories then current. In the published description of these
forests (Holloway, 1946) reference was made to the fact that, in their distribution, the forest types represented in the area could not wholly be accounted for in terms of the static factors of site. The full significance of this was, however, not then recognised and if the account were to be re-written to-day greater emphasis would be placed on the phenomena indicative of forest, change and instability. The Longwood survey of itself, nevertheless, did not open up any really new ground for theoretical consideration but it did introduce an element of doubt which lead to more critical study of forests later surveyed. And the Longwood survey did destroy all academic faith in the accuracy of forest descriptions already published. These old accounts proved reasonably accurate for forest areas readily accessible from tracks and roads but were grossly inaccurate for the comparatively inaccessible bulk of the forest. Other forests were accordingly examined with a mind wholly freed from prejudice in favour of earlier work.
On completion of the Longwood survey, the work of the survey was extended to cover the larger forests stretching westwards from the Waiau River (see Locality Map 1); and select examples from these West Waiau forests probably afford the best possible introduction to study of the South Island forests as a whole.
The Alton Reversals
The West Waiau forests had previously been described, in vague terms only, as beech forests with a strong podocarp element, but closer inspection showed that a confused ad-mixture of many distinct types of forest was present in the area. And these many types were, at first glance, distributed quite haphazardly.
The normal expectation where beech and podocarp forest types co-exist within a region is for the podocarp stands to be developed at lower altitudes or on slopes of warm aspect with beech forest occupying the higher ground and slopes
of cold aspect. Silver beech, Nothofagus menziesii, is generally regarded as more mesophytic than mountain beech, Nothofagus cliffortioides; and matai, Podocarpus spicatus, as more mesophytic than rimu, Dacrydium cupressinum. But in the West Waiau forests these normal expectations were everywhere upset Examination of Diagram 1 will indicate the extent of the divergence between the anticipated and the actual in one particular locality, the diagram representing, in somewhat idealised form, a line transect from the valley of the Lillburn, across the Alton Valley, to the valley of the Groveburn.
To the south of the Alton Stream there is, first of all, a narrow riparian fringe of mountain beech/silver beech forest but mountain beech does not extend far up the lower, sunny, north-facing slopes which carry silver beech stands through which are scattered a few rimu and other associate podocarps. These latter increase steadily in abundance until, on the upper hill slopes, rimu is the physiognomic dominant with but a sparse representation of silver beech. On the ridge crest along the Groveburn-Alton interfluve pure stands of podocarps are found, tall straight rimu of excellent form, vigour and quality with scattered miro, P. ferrugineus, and Hall's totara, P. hallii, over a light understory of kamahi, Weinmannia racemosa, and rata, Metrosideros umbellate. And on the very highest hill-tops there are occasional groups of very old, massive, true totara, P. totara, with, rarely, a few defective malformed matai.
Across the interfluve, on the shady cold aspect slopes falling toward the Groveburn podocarp forest persists; but these stands are markedly different to the ridge crest stands already described. On the ridge crests the dominant rimu appear vigorous and there is a fair representation of the younger age classes. The stands are well to fully stocked. But on the shady Groveburn slopes the rimu present are typically large over-mature veterans which stand, widely spaced apart, over a ‘jungle’ understory of large, twisted, malformed rata, kamahi, and other secondary scrub hardwood species. In these stands there is little, if any, podocarp regeneration and there are very few, if any, pole rimu, young trees in the 100–250 year age class. There may be a few pole size miro or Hall's totara but these generally appear stagnant and defective.
Silver beech appears in the stands again a little above the floor of the Groveburn Valley, is dominant across the valley floor, and persists a short distance up the warm north-facing Groveburn slopes; but there is soon another abrupt change into pure podocarp forest, this time of comparable quality to that developed on the Alton-Groveburn ridge crests. The dominant rimu in these stands are generally of slightly smaller average diameter than are those found on the ridges and the stands are more heavily stocked. Rata and kamahi are present as low shrubs only or are altogether absent.
To the north of the Alton Stream the cold aspect slopes above the riparian mountain beech/silver beech stands carry pure silver beech forest with scattered rimu appearing toward the Alton-Lillburn ridge crest; and, on the highest hilltops, there are a few pockets of pure podocarp forest, rimu again dominant, of a quality intermediate between that of the stands developed on the warm and cold aspect slopes of the Groveburn respectively. To the north, again, on the warm aspect slopes falling to the Lillburn Valley, silver beech is the universal dominant on the upper slopes but mountain beech soon appears in the stands and, downslope, steadily increases in abundance until, on the lower slopes, it is generally
dominant. Even here, however, there are a few scattered small, but old, rimu though never younger pole rimu or trees of any vigour.
Now this distribution pattern is most peculiar, running directly contrary to the pattern which would normally be expected on the basis of a study of the site requirements of the several major species involved; and there are other peculiar items to note. Where silver beech stands abut upon one or other of the podocarp forest types then any canopy destruction, by axe, fire or wind, is followed by extension of the area occupied by silver beech but never by re-development of the podocarp stands. Where podocarp forest is logged, burnt or wind-thrown and there is no local seed source of silver beech, there is immediate prolific development of the podocarp associate scrub hardwoods, rata, kamahi and the rest, but never any regeneration of the podocarps. Where silver beech and mountain beech are both present, all stand regeneration following logging or following any natural disruption of the forest canopy shows mountain beech dominant even though this species, previously, may have been a minor stand constituent. Silver beech seedlings and saplings will outgrow and suppress the seedlings and saplings of the podocarp associate hardwoods both in the mixed beech/podocarp stands and along the ecotones between pure beech stands and pure podocarp stands. Mountain beech seedlings and saplings will outgrow and suppress silver beech juveniles wherever they occur together. And podocarp regeneration fails, uniformly, on all sites.
Is it possible to explain all these many distributional anomalies and these features of relative aggression as occasioned by local factors of site? The whole transect covers but a few miles and lies across the mean path of the prevailing winds. The effective rainfall might be a trifle lower on the Lillburn slopes to the north than on the Groveburn slopes to the south since the former are somewhat more exposed to the north-west, winds from this quarter commonly blowing dry and hot in summer, but such differences are slight. The mountain beech in the riparian stands bordering the Alton Stream do occupy the sites most subject to heavy and persistent winter frosts but frosts are not severe on the sunny lower slopes above the Lillburn; and mountain beech is not found on the frost subject river flats along the Groveburn. It could be argued that the ridge crest podocarp stands occupy relatively warm sites above frost level but, as mid-winter inspections show, frosts can be heavy on these ridges; and in any case such an hypothesis fails to explain the occurrence of the podocarp stands on the cold aspect Groveburn slopes. It would seem improbable that tenable explanations can be derived from consideration of the climatic factors of site.
Edaphic factors? All soils, with few exceptions, are derived from the same geological strata, slightly sandy late tertiary siltstones. the exceptions being local outcrops of uncemented sand-stones in the lower Groveburn Valley and local remnants of a former cap of fluvio-glacial gneissic gravels on the ridge crests. And in both cases the forest type ecotones slice across the lines of outcrop and are not affected thereby. There are minor differences with respect to the secondary species of the forest floor and the ridge crest podocarp stands do occupy a substantial proportion of the ridge crest gravels but this would appear to be a simple consequence of the topographic position of the gravels, not an example of soil type control of forest type distribution. On the ridge crests podocarp stands can be found away from the gravels and beech stands can be found on the gravels.
Elsewhere in Southland, vide infra, podocarps do exhibit a preference for fluvio-glacial gravel terrace soils but this soil factor does not appear to exert a controlling influence in the present case. Throughout the area under consideration the variations in soil profiles appear to be no greater than can rationally be accounted for by differences in the amount and quality of the forest litter. That is to say that it would appear that the forest has more influence on the soil than the soil has on the forest.
All possible explanations were considered and argued during many months spent within this area of forest but no explanations appeared satisfactory until it was observed that, in those instances where silver beech trees persisted upslope from the Alton Stream to the crest of the Alton-Groveburn interfluve, silver beech was also present along the margins of streams draining from these points to the Groveburn, linking up, through the podocarp stands, the Alton and Groveburn silver beech forest types. And similarly, where occasional mountain beech were established at low points along the Alton-Lillburn interfluve in such a position that seed could be shed into streams flowing to the Alton, mountain beech occurred down these streams linking up the Lillburn and Alton mountain beech stands.
These observations called for immediate consideration of methods of seed dispersal and species migration. It appeared that though the seed of most podocarp species may be distributed by birds, seed of the beech species is wind distributed. Investigations showed that all seed from a single tree of either mountain or silver beech normally fell within a distance from the tree equal, more or less, to the height of the tree, in exceptional cases and down wind within, at most, two to three times this distance. Mass migration of these species across country must, therefore, be an extremely slow process. But seed shed into rivers and streams can be carried long distances in a single season and, since all the beech species pioneer newly eroded or bared ground with great facility, water carriage of seed can lead to rapid migration of species down water-ways with resultant establishment of fresh nuclei from which slow migration by wind dispersal of seed can again take place in direction away from the streams.
To reconsider the situation in the Alton and adjoining valleys: Diagram 2 show the forest type distribution in plan.
The first assumption to be made is that, at some distant date, the entire area was occupied by podocarp forest, rimu dominant but with local development of matai/totara forest types and with a persistent source of silver and mountain beech seed somewhere to the north. Consequent on some variation in regional climate, favourable to the beech species but unfavourable to the podocarps, silver beech invaded the stands by water carriage of seed down the Lillburn, the only stream heading back into the mountains where survival of beech seed sources during a long period of podocarp favourable climate was most probable. Migration upslope from the Lillburn into the now less vigorous podocarp stands would proceed slowly until seed was shed into the headwater tributaries of the Alton. Following rapid migration down this waterway, silver beech would again migrate slowly upslope both to the north and to the south with the result that the last pockets of podocarp forest would be “pinched out” along the crest of the interfluve. And since, in many cases, it would be expected that seed from the north would reach the highest ground before seed from the south, the last pockets
of podocarp forest should be left in a slightly eccentric position on the lee, or south, of the highest hill-tops; and this slight eccentricity is, in fact, a feature of these isolated stands.
To the south of the Alton Stream silver beech would appear to have reached, but recently, the crest of the interfluve at its lowest points and to have spread from these points, by water carriage, through the stagnating podocarp stands on the shady Groveburn slopes, down to the floor of the Groveburn Valley where it has, as yet, occupied little more than the valley floor. In the case of this valley it is probable that the Alton silver beech seed source has been supplemented by seed reaching the headwater streams from the Rowallan Valley to the west but this complication in no way vitiates the main argument.
In the wake of silver beech, possibly following further climatic variation, mountain beech invaded the area; and the same general migration pattern is reproduced though mountain beech seldom displaces silver beech entirely since their site demands are more nearly equal. Mountain beech may be said to have infiltrated slowly through the silver beech stands of the Lillburn slopes until, in turn, its seed was shed into the Alton tributaries with rapid consequent reproduction of the characteristic, finger-like, riparian invasion processes. In the Alton mountain beech has, to date, occupied little more than the valley floor though occasional groups of trees are established some distance up the sunny north-facing slopes.
The ridge crest podocarp stands and the podocarp forest on the warm Groveburn slopes are still moderately well in harmony with local climates. The aspect is exceptionally favourable in the one case while, in the other, the more favourable soil conditions found on the ridge crest gravels may tend to outweigh adverse climatic factors. The vigour and form of the individual rimu suggests that there has been some regeneration of the stands over the past several centuries and a few seedlings and saplings still occur though never in sufficient numbers for full restoration of the podocarp canopy as veteran trees decay and fall. But in the podocarp stands on the cold aspect Groveburn slopes there has been no effective regeneration of the podocarp dominants, particularly of rimu, for many centuries and, as the canopy has opened up through decay and wind-fall, the secondary scrub hardwoods, in the absence of a beech seed source, have run riot.
In this way the facts of forest type distribution are, on the basis of one hypothesis, susceptible of neat explanation and the same hypothesis accounts satisfactorily for present behavioural peculiarities displayed by the species concerned. But this is by no means proof of the validity of the hypothesis and its application as above might well be considered simply an ingenious exercise in imagination. It may be that the many demonstrated peculiarities can be explained as the cumulative result of many local variations in site. But these Alton Reversals do not stand alone. There are other links in the chain of evidence. Moreover, it is well worth stressing at this point that there is no more proof that climates have remained stable over long periods of time than there is proof to the contrary.
The Rowallan Reversals
In the Alton system, the grain of the land, the drainage pattern, lay across the postulated migration path of the incoming beech species. What forest type distribution pattern could be anticipated where drainage patterns parallel migration
paths? The pattern to be anticipated in such a case, assuming the above explanation of the Alton situation to be subsequently correct, should be that shown in Diagram 3.
Here we assume that silver and mountain beech are invading a podocarp forest region from the north and that, in turn, seed of these two species is shed into the headwater streams of parallel rivers flowing from north to south. A stage should, in course of time, be reached with the remnant podocarp zone widening out from north to south for several reasons. In the first place, downstream toward the coast, an area of milder coastal climate will be entered and the podocarp stands will be better favoured. The advance of the beech species will be retarded Secondly, there will probably be an appreciable time lag in between riparian establishment of the beech species along the upper reaches of the rivers and their effective establishment downstream. Effective establishment will depend very largely upon deposition of seed in bulk and it is probably safe to assume that most of the water-borne seed will have come to rest long before the lower river courses are reached. In any case, establishment will take place more readily where stream bank erosion is more rapid, i.e, upstream, than along the heavily forested lower flood plains.
On the upper hill slopes, below the ridge crest podocarp stands, mixed silver beech/podocarp stands should be present, the podocarp element decreasing downslope with the incoming of mountain beech. And, from north to south, there should be a steady fall in the altitudes reached by both silver and mountain beech. Well to the south mountain beech should not be found far from the river banks and the silver beech/podocarp stands will occupy the whole of the lower slopes and probably the greater part of the river flats.
This exact situation was encountered where, to the west of the Alton and Groveburn Valleys, the two branches of the Rowallan River flow parallel to one another from their sources on the Lillburn-Rowallan watershed to their confluence a few miles from the sea, the actual distribution of forest types being shown in Diagram 4.
The close degree of correspondence between the actual and the anticipated will be readily apparent. There is a certain asymmetry noticeable with respect to the distribution of mountain beech, the mixed silver beech/mountain beech forest type being better developed by far in the West Branch of the Rowallan than in the East Branch. This would seem to be due to the fact that mountain beech could reach Point A, from the Lillburn, by a more direct route than could be followed to Point B. To reach Point B an extensive bog pine (Dacrydium bidwillii) swamp had to be by-passed, edaphic conditions being unsuited to the direct passage of the species. In other words, mountain beech seed was shed into the West Rowallan some considerable time before reaching the East Rowallan.
The ridge crest podocarp stands are broken, to the north, by silver beech penetrations across the lowest points along the interfluve and the most northerly ridge crests are occupied, not by pure podocarp stands but by mixed silver beech/podocarp stands. The ridge podocarps are generally comparable in condition and in quality to those of the Alton-Groveburn interfluve though the stands are not so heavily stocked largely on account of the more strongly gullied nature of the terrain. In the south, however, where the podocarp stands expand out across the south-facing slopes of the interfluve above the confluence of the
two branches of the Rowallan, the stands are equally as degenerate as those of the shady Groveburn slopes despite their proximity to the coast. A few pockets of disintegrating matai/totara forest also occur on these cold slopes.
To the south of the confluence of the two streams, a further type of podocarp forest is found. This occupies coastal fluvio-glacial gravel terraces and on these terraces the podocarps, rimu again dominant, appear very much more vigorous. In these stands there is found a wider range in age classes than elsewhere together with a fair representation of rimu advance growth, poles and saplings. Nowhere, in the south, save on soils developed from these gravels, does the rimu forest display equal vigour or appear so nearly normal in its age structure. Nevertheless, even here, tongues of beech forest, both of silver and of mountain beech, penetrate to the coast. These beech stands spread away from the rivers occupying all ground where the gravels have been thinned or removed by erosion exposing the underlying siltstones and, coastwise, along the cliffs exposed to salt spray. But silver beech does tend, also, to enter the podocarp stands on the terraces themselves. Not even these, therefore, can be considered fully stable under existing conditions.
The Mid-Slope Podocarps Of The Longwood Range
One outstanding feature of the Longwood forests is the frequent occurrence of restricted pockets of podocarp forest (rimu) on the mid-slopes of the range particularly along the eastern fall above the Pourakino Valley. These pockets are wholly surrounded by silver beech stands or by mixed silver beech—podocarp types. Their occurrence could be explained very simply as due to the comparative warmth of the mid-slopes, the sites lying above the line of heavy winter frost and below the limits of normal winter snowfall; and in some instances such an explanation would appear perfectly sufficient. But, if this is the entire explanation, how is the presence of old veteran rimu at lower levels to be explained. These veteran trees are found throughout the silver beech stands of the lower slopes and valley floors, younger podocarps seldom being present. And there are many other problems to be solved.
True totara is, to-day, represented in the Longwood forests by one group of very old defective trees though logs of this species, the heartwood still being sound, are more widely distributed. Why is mountain beech unrepresented in the forests on the upper slopes of the range though present around the western lowland margins of the forest? Why, in many areas, has there been evident replacement of rata by silver beech, many trees of the latter species straddling fallen logs of the former? Why is matai, throughout these forests, universally defective, stagnant, and incapable of reproduction? All these problems, and others, are susceptible of ready explanation once it is assumed that the regional climate has, comparatively recently, deteriorated, favouring the cold climate silver beech at the expense of the more mesophytic podocarps.
We must assume, first, a distribution of podocarp and silver beech forest as shown in Diagram 5, a distribution effective when the climate was very much milder than it is to-day. The lower ground was wholly occupied by podocarp forest, rimu generally dominant though with totara. matai and kahikatea (Podocarpus dacrydioides) forest types developed on sites of favourable character. Silver beech was restricted to a cap on the summit of the range with, perhaps, evanescent communities established along the stream and river banks. That, is
to say that we have assumed a distribution pattern no longer common in the far south though commonly found to-day in the north. Following regional climatic deterioration the more mesophytic podocarps, matai and true totara, were virtually eliminated and are now represented by a few derelict survivors on sites of particularly warm aspect or on sites where edaphic factors are particularly favourable Kahikatea, which in the old forests grew vigorously on the hill slopes, survives through facultative adaption to swamp conditions and is found, in association with silver beech on swampy reaches of the valley floors. Silver beech spread rapidly down all streams from the seed sources on the upper slopes, and, more slowly, out across the valley floors and up the valley slopes. Initially, there would still be some regeneration of the podocarps on such sites and survivors from this last strike of podocarp seedlings now form the old podocarp standards scattered through the lowland beech stands.
Silver beech spread, also, slowly downslope into the podocarp stands and outwards from the streams so that, eventually, the podocarp stands have been ‘pinched out’ along the midslopes (see Diagram 6). Where these slopes are relatively frost free and other site factors are exceptionally favourable, this replacement of the podocarps by silver beech might be halted before completion and this would seem to be the case on certain western slopes of particularly warm aspect where the soils are also unusually good. On these exceptional sites the residual podocarp stands are well stocked and there is a fair representation of age classes but, more typically, the midslope podocarp stands are now degenerate. There are no persistent seedling or sapling podocarps present and, in many cases, there is an understory of young vigorous silver beech.
All stages in these many processes of forest re-adjustment can be traced. The changes do not proceed uniformly over the entire area but comparable re-adjustment patterns are traceable throughout In areas where the former (hypothetical) podocarp forests completely occupied the hill-tops leaving no seed source of silver beech at higher levels, degenerate types of podocarp forest still extend to the summits. Replacement wholly from below is a very slow process unaided by water carriage of seed. There is a good example of this along the line of out-lying hills to the east of the Pourakino Valley. These low hills carry, or carried before logging, podocarp forest of a character intermediate between the two Groveburn types already described. To the west there is a slow infiltration of silver beech up-hill from seed sources along the Pourakino River and, in one locality, silver beech has crossed a low saddle and has spread down a stream draining to the Aparima River to the east.
Two small pockets of silver beech do occur on the crest of these hills. One of these is restricted, more or less, to the area of outcrop of a norite, surrounding strata being largely more strongly basic volcanics. This pocket of silver beech might, therefore be interpreted as a remnant which has survived throughout the full period of maximum podocarp forest expansion, owing its survival to local edaphic factors. Down all streams draining from this area riparian stands of silver beech extend through the surrounding podocarp forest and these riparian stands are fringed by vigorous young silver beech pole stands.
The second such pocket lies toward the centre of a broad flat ridge crest where the soils tend to be swampy. Silver beech may here have survived as a species of swamp forest No streams drain from the area and no marked outward
expansion has taken place though there is a tendency toward peripheral spread into the adjoining podocarp forest.
Local factors of site, soil, drainage, aspect and so on, may influence the rate at which forest re-adjustments proceed in response to variations in regional climate. They may retard the processes of change or even, in exceptional cases, bring them to a halt; but the present distribution of forest types and species is primarily a matter governed by climate, not the climate of to-day nor yet the climate of yesterday but something intermediate. Both the climate of to-day and the climate of the past must be considered in analyses of distribution patterns and, in their finer details, these patterns may frequently be distorted by local accidents of topography or soil, by the presence or absence of physical or biotic barriers, the presence or absence of migration paths, factors which have contributed toward the preservation of seed sources of potential invading species or which tend to facilitate or retard their spread.
Biotic Barriers, Geological Accidents And Seed Sources
Several instances might be noted where incoming species have been effectively prevented from reaching sites where conditions are now such that these species could be expected to flourish.
The absence of mountain beech from the upper slope stands of the Longwood Range has already been noted. Mountain beech is present around the western lowland fringes of the forest, riparian mountain beech stands occurring along both the Orauea and Waiau Rivers both of which drain from high country to the north carrying mountain beech forests. But no mountain beech is found on those sites at higher altitudes to which it would appear better adapted than the silver beech now in occupation. If, however, the podocarp stands once extended almost to the summit of the range leaving but a small residual cap of silver beech then, under these conditions, survival of mountain beech seed sources would be improbable. Seed was available, following the climatic change, from the rivers to the west but mountain beech could only reach the intrinsically more favourable upper slope sites by penetration of the heavy podocarp and podocarp/silver beech stands of the lower slopes. This must be an extraordinarily slow process for the migration path lies up-hill without favour of water-carriage of seed; and seedling establishment must be in the face of intense competition from species already on the ground and well adapted to the site.
Several small groups of mountain beech have been found within the podocarp and podocarp/silver beech stands of the lower slopes at distances up to a mile or so from the river banks; and these chance groups present the appearance of having originated in local forest clearings where temporary relief from competition was obtained. Should present climates remain stable for a long period of time then the probability is that mountain beech would, at length, reach the upper slope sites to which it is suited but, so far, the lower slope forests have proved an effective migration barrier.
The second example is taken from forests lying immediately to the west of the Waiau River. Both silver and mountain beech are absent from the hill complex forests lying between the Waiau River and the lower Groveburn Valley, i.e, from the area centred on Mason's Hill Silver beech is present in the Groveburn Valley on riparian sites but could not, in the time available, have spread
from these sites to the hill crests since, as already suggested, it is but a recent entrant into the Groveburn. But both mountain and silver beech are, and probably for a long period of time have been, established along the terrace margins bordering the Waiau River. Their absence from the hill forests is attributable to the biotic barrier of relatively stable podocarp forest which, previous to logging, occupied the main gravel river terraces.
Both species did penetrate the barrier in part. They spread slowly across the terraces occupying pockets of swampy ground where competition with the podocarps was not severe or, temporarily, local wind-fall areas; but they did not penetrate any distance up the lower hill slopes where light sandy soils carried vigorous podocarp stands with dense understories of ferns, shrubs and small broad-leaved trees. They were unable to reach the hill crests where site conditions were most suited to them and, with the virtual elimination of the podocarps following the climatic change, the hill crest stands have degenerated into scrub forest of stunted rata and kamahi. On comparable sites elsewhere, seed sources being available, either one or both of the beech species invade, suppress and eliminate the rata and kamahi stands with great rapidity.
In the forests immediately to the west of the Waiau River and in the Long-woods, migration patterns are relatively straight-forward. There are comparatively few complications arising through the operation of biotic or other effective barriers to migration In other forests, however, such factors assume greater importance. They may even mask entirely the normal processes of change, distorting out of recognition the usual patterns of forest re-adjustment.
The gravel river terraces flanking the Wairaurahiri River carry a complex admixture of forest types though the basic factors of site are remarkably uniform throughout. Near the coast, the terraces carry rimu stands similar to those developed on the Rowallan coastal gravel terraces as already described. Inland, the terraces may carry rimu stands, silver beech stands or mountain beech stands, or the terrace stands may be composed of any two or all three of these species in any proportion. At first sight there would seem to be no good reason for this marked heterogeneity but it is possible to account for it in terms of the hypothesis of recent climatic variation.
It has been seen that rapid invasion of an area of podocarp forest by the beech species, following a climatic change adverse to the podocarps, is dependent on water carriage of seed of the incoming species. Now the watershed flanking the Wairaurahiri Valley, the Hump Ridge, is composed of two main types of rock, basal coal measure sandstones and coarse conglomerates; and, on the upper hill slopes, silver beech is the dominant or only species on the conglomerates with mountain beech the dominant or only species on the sandstones. Where streams crossing the river terraces drain conglomerate slopes. therefore, the seed brought in is largely silver beech seed and the forest on the terrace will be silver beech/podocarp forest. Where streams drain sandstone slopes the terrace stands are mountain beech/podocarp stands Mixed mountain beech/silver beech/podocarp stands occur wherever seed of both beech species was immediately available and the pure podocarp stands occupy the centres of the larger terraces remote from the streams as well as all terraces untraversed by any streams.
To the north, near Lake Hauroko, the position is complicated by recent faulting which has resulted in slight headward tilting of tributary streams with con-
sequent secondary changes in forest development following changes in terrace drainage, and recent river deposits have been colonised by a wide range of species. These secondary effects superimposed on the main trends in forest development have produced such apparently abnormal forest types as the kahikatea/mountain beech/kowhai (Sophora microphylla)/manuka (Leptospermum scoparium) type, but the main trend remains clear, a progressive replacement of podocarp forest by beech forest. Local variations on the theme depend upon the operation of purely local factors of site but sometimes, also, upon the operation of factors wholly extraneous to the site. In the present instance these extraneous factors were geological factors governing the type of seed supply. The type of forest now established on any particular river terrace depends not on any of the regular basic factors of site but upon the extraneous factor, the nature of the terrain drained by the terrace streams.
In many cases, therefore, it is largely a matter of accident which species arrives first, and in many instances the incoming species may not be that which is best suited to the site. In the Wairaurahiri Valley the terrace podocarps are on many terraces, in process of replacement by mountain beech though, on sites of this quality, silver beech would seem to be the obvious successor species. In all such cases even those forest types now in course of development will not be the ‘climax’ types for the site under existing climatic conditions. Some of them may be but it will definitely be unsafe, in any instance, to assume that this is so. The many processes of forest evolution are conditioned and controlled not only by climatic factors, but by accidents of geology and geomorphology.
One further example from the forests of the Hump Ridge might be described In general, on the Ridge, the midslope podocarp stands have been eliminated leaving a midslope zone of mountain beech/silver beech forest containing a strong podocarp element; but at the extreme southern end of the Ridge near Sandhill Point, a distinct type of podocarp forest survives at comparatively high altitudes. 1,500 to 2,000 ft. above sea level. The type is characterised by the presence of small, stunted rimu with stunted Hall's totara co-dominant. Its survival is possibly attributable to some peculiarly favourable local site factor complex but if Diagram 7 be consulted, it will be seen that the hill-crest occupied by the stands lies, at its highest point, below the postulated ancient altitudinal limit of the podocarp forests. Invasion of the type by either of the beech species must proceed uphill from the saddle, a slow process possibly rendered slower by local operation of podocarp favourable factors.
The lower slopes below the ridge crest podocarp stand carry podocarp forest of a type similar to that developed on the Longwood midslopes and these stands merge into coastal gravel terrace stands developed near the shore. The ridge crest stands could not, therefore, be invaded by other of the beech species directly from below. Invasion on the east (the aspect illustrated in the Diagram) could only proceed downstream from sandstone-conglomerate areas on the main upper slopes of the Hump Ridge followed by slow movement along the coastal cliffs and up into and through the coastal terrace podocarp stands Such a movement can be demonstrated on the ground but it is very slow in its latter stages.
To the west of the Hump Ridge, silver beech could enter by a circuitous path from conglomerate slopes below the main summits, a rapid series of movements down secondary streams linked by intervening slow movements across the sharp
ridges between the streams, and this movement, also, can be demonstrated on the ground. Fingers of silver beech forest extend down all streams draining from the main summits and, spreading out from these riparian stands, small pockets of young silver beech extend upslope into the high altitude podocarp stands. Mountain beech, however, is unable to invade the podocarp stands from the west since it is effectively sealed off by a barrier of silver beech forest on soils derived from the conglomerates.
The real problem in the case of these high altitude ridge crest podocarp stands is not the problem of their presence but the problem of their condition. Why have these stands persisted as podocarp stands without replacement, as usual under such circumstances elsewhere, of the podocarps by rata, kamahi or other scrub hardwood species? The answer is not known but it would seem that an edaphic factor is responsible. Podocarp forest of this unusual type has only been found on soils derived from this same series of coal measure conglomerates.
Silver beech forest on the conglomerates forms a barrier through which mountain beech can spread only by water carriage of seed. Comparable conditions obtain on many lime rich soils. Outcropping limestones or lime rich sandstones, e g., Helmet Hill, Dean Hill, and Diggers Ridge, to cite West Waiau examples, commonly carry on their dip slopes pure stands of silver beech though mountain beech may be dominant or co-dominant on adjacent sandstones, siltstones or alluvials and may even be present on the dry limestone escarpments. Distribution and migration patterns are distorted by these lime rich soils and, failing penetration by water carriage, effective barriers to the further spread of mountain beech are created.
Up to this point in the discussion it has been tacitly assumed that the beech species did not survive the podocarp forest period save in high altitude forests. This was undoubtedly the general rule but there were one or two exceptions to be noted In discussing the mid-slope podocarps of the Longwood Range it was
suggested that, throughout the era of maximum podocarp forest expansion, there may have existed ‘evanescent silver beech communities of pioneer character’ on riparian sites. Now it would be possible for these ‘evanescent communities’ to outlive the remnant high altitude seed sources from which they took their origin. Through continued establishment and re-establishment on fresh sites, eroded stream banks and fresh alluviums, it would be possible for them to persist long after the disappearance of the primary seed sources. There would be a continued tendency toward downstream drift of these detached riparian communities with the final survivors maintaining a precarious foothold in the hostile climatic environment at that date obtaining in the lowlands.
No definite examples of the operation of a survival mechanism of this type have been traced in the forests of Western Southland though the operation of such mechanisms is suspected in several instances. In Otago, particularly in the Dunedin District, several of the small silver beech forests do appear to have taken their origin from casually surviving riparian stands and to be without connection with surviving high altitude silver beech stands. But clear cut examples are not, to-day, to be found in the South Island though many good examples are encountered in North Island forests where the events of the more distant past have not been so thoroughly masked by rapid recent changes in forest type and species distribution. Two North Island examples, only, might be instanced. Firstly, there is the case of the isolated riparian silver beech stand on the eastern (Lake Taupo) slopes of the Hauhangaroa Range as described though not explained by Poole (1950); and secondly, there are the riparian stands, several beech species being represented, of the Mamaku plateau to the north and east of Rotorua. These North Island riparian beech communities admit no other interpretation of their origin and continued existence than that advanced herein; and it must therefore be anticipated that comparable survival mechanisms were once operative in the south. Even in the case of the Alton and Rowallan Reversals, there may have been some survival of beech seed sources along the streams throughout the podocarp forest period. It is not necessary to assume such survival in order to explain the situation developed to-day but it was possible. It would not invalidate the account given herein of the processes of forest re adjustment but would mean, only, that the present account has been somewhat over-simplified. Survival of beech seed sources on riparian sites within a podocarp region would, when coupled with entry, by water carriage of seed, of the beech species possibly result in the speeding up of all re-adjustment processes. The basic patterns of change would not be greatly affected.
Mountain and silver beech could also survive on lowland sites throughout a climatic era favourable to podocarp forest development as species of bog forest. One possible instance has already been described from the forests to the east of the Pourakino River, Longwood Range, and many other cases will be described later. Survival of beech seed sources in lowland bogs is by no means an infrequent phenomenon but is one which commonly provides the key to an understanding of present type distributions.
Not every item of forest type distribution will be wholly explicable in terms of the one simple basic hypothesis; straightforward examples such as those described from the Longwood and West Waiau forests will inevitably be few; secondary hypotheses must frequently be invoked before distribution patterns can be understood in detail. The basic patterns will commonly be distorted or modified
through chance survival of lowland seed sources for the incoming beech species, through operation of effective migration barriers, or through operation of what have herein been called geological or geomorphological accidents. The exceptions to the general rules of forest type distribution, as interpreted in the light of the hypothesis of recent climatic change, will be many; but these exceptions will not necessarily be destructive of the validity of the basic hypothesis.
The Coastal Terrace Podocarps
Since it would appear that, at some not far distance date, podocarp forests flourished on those hill sites in Western Southland where, to-day, the podocarp stands are degenerate and are in course of replacement by rata/kamahi stands or by beech stands, we have been compelled to assume a recent change in regional climate in direction away from the podocarp optimum and toward the beech optimum, i.e., a change to colder and possibly also to drier conditions. This regional change must, at the same time, have had some effect on other regional forests.
The coastal gravel terraces, to-day, support dense podocarp stands of a general vigour contrasting markedly with the over-maturity or senescence of the hill podocarps. What was the nature of the forest cover on the terrace lands when the hill podocarp stands were at the peak of their vigour?
In virgin coastal terrace podocarp stands to the west of the Wairaurahiri River occasional small, roughly circular pockets of forest may be distinguished. In these pockets the dominant rimu are of small diameter and heavy stocking, small, straight, pole-sized trees of younger age than the rimu in the surrounding forest. Such pole stands, as they occur in comparable forest types on the Westland gravel plains, have been regarded in the past (Hutchinson, 1928) as indicative of profuse regeneration in areas of wind-throw. This view is undoubtedly correct in certain instances. The old, moss covered, stump and log mounds remain in evidence. But in many other cases the forest floor, within the pole stands, is clean and level. The pole groups originated in some other manner. To the west of the Wairaurahiri River the mechanism becomes clear.
The pole groups occur with greater frequency and are larger. At a certain point in size they open out in the centre revealing a pocket of bog forest characterised by the general dominance of yellow-silver pine (Dacrydium intermedium) with manuka, various epacrids, and other heathy plants over a soil cover of dense sphagnum moss. Around the periphery of the bog forest pockets there is, commonly, a narrow marginal zone of young rimu in the sapling or early pole phases of growth. It is now possible to turn back to the pole rimu groups without bog centres and to find within them, in many instances, occasional dead or moribund yellow-silver pine or, more rarely, dead stems of manuka. These pole groups may, therefore, be considered representative of the final stages of the closing in of rimu forest around and over pre-existing yellow-silver pine bogs; in other words, there is good cause to believe that, in the past, the coastal gravel terraces carried, not rimu forest, but yellow-silver pine bog forest.
The bogs would not be continuous over the entire extent of the terrace lands but would be broken up by a network of rimu dominant stands occupying terrace margins, stream banks, inter-terrace slopes and all other local dry sites; and when, consequent on regional climatic variation, the hill podocarp stands
entered into a long period of decline and stagnation, rimu, simultaneously, advanced out across the terrace bogs.
In some localities these processes did not reach completion. Possibly as a consequence of a further deterioration in regional climate, or for edaphic reasons, the central portions of several of the larger bogs remain unoccupied by rimu. There is some peripheral colonisation of these bog remnants by rimu under present conditions but the young rimu stagnate early. Surviving seedlings and saplings display excessively slow rates of growth with a high incidence of malformation It would appear impossible for these bog margin sapling stands to develop into mature stands of the high quality characteristic of the terrace rimu stands as a whole.
To the west of the Waitutu River the colonisation of the terrace bogs by rimu was incomplete before invasion of the terraces by the beech species began. In these forests the residual bogs now carry stunted silver and mountain beech in addition to the more usual bog forest species and the peripheral stands contain, in addition to the usual pole rimu. a strong and vigorous beech forest component On the drier ground, to the west of the Waitutu, the forest canopy is very broken Rimu and silver beech are co-dominant, both being heavily defective and overmature though the rimu are of considerably greater age than the silver beech. Throughout these stands all light pools are filled with seedling, sapling or pole thickets of mountain beech and this species is everywhere aggressive.
In these forests, in other words, the swing from podocarp forest to beech forest began before the occupation of the coastal terraces by rimu was completed. All the several changes, yellow-silver pine bog forest to rimu forest, to silver beech forest, to mountain beech forest, have been telescoped. Possibly only in its initial phases did the regional climatic change favour the advance of the podocarps across the terrace lands; and it is likewise probable that the rapidity of advance of the beech species is to be accounted for through their survival throughout the previous climatic era, in the bogs. At the same time local edaphic factors must have played a very significant part in determining local trends in forest evolution. On high level gravel terraces, 900 to 1,200 ft. lying between the Wairaurahiri and Waitutu Rivers, the soils are mature podsols with strongly developed impermeable iron pans. On these ‘plateaux’ the forest is stunted. The widely spaced rimu seldom exceed 30 to 40 ft. in total height though they may be of considerable girth and possess immense spreading canopies. They stand out over an impenetrable tangle of mountain and silver beech with yellow-silver pine, bog pine (Dacrydium bidwillii), pink pine (Dacrydium biforme), manuka, epacrids and other shrub species common to bog forest. The forest floor is carpeted with deep moss, bryophyte cushions, pygmy pine (Dacrydium laxifolium) and other mat and cushion plants. On these mature podsols, under present climatic conditions, neither the podocarps nor the beech species could attain their optimum development.
The West Waiau forests, particularly the forests to the west of the Wairaurahiri River, are patchwork forests. In them, forest types in all stages of evolution in response to regional climatic changes and in response to local edaphic trends are in evidence. The patterns of forest re-adjustment are commonly distorted in accordance with local topographic or geological factors but, in their full structural complexity, the forests can only be accounted for in terms of the
hypothesis of climatic change. Any isolated abnormality can frequently be ‘explained’ without any appeal to such a radical hypothesis though no such an explanation can be extended to cover the full range of abnormalities in evidence; but in the climatic change hypothesis we have a relatively simple and straightforward explanation for even the most complex distribution patterns.
To detail one last example, a simple one, from the coastal terrace forests; where silver and mountain beech are present on the ‘plateau’ gravels described above in such a position that seed can be shed into the headwaters of streams flowing down across the coastal terraces, both beech species are represented in the terrace stands. But where the terraces are untraversed by such streams the beech species are absent. Where the beech species are present in the forest on the terraces, the stands along the coastal cliffs are beech/podocarp stands containing little rata. Where the beeches are absent rata is co-dominant with the podocarps along the cliff tops. The precise character of the coastal stands is dependent, not upon purely local factors of site but upon the degree of proximity of the site to seed sources of mountain and silver beech. And replacement of the rata in the rata/podocarp stands by the beech species through migration along the shore is slow but sure. All factors of site in respect to these coastal stands remain constant throughout save only the factor of seed source proximity. Is it possible to explain the distribution of the rata/podocarp and the beech/podocarp stands without recourse to the hypothesis of climatic change?
Matai, an Important Climatic Indicator Species
No attempt has been made in this account of the forests of the extreme southwest of the South Island to describe them in detail. A few chosen and critical items of forest type distribution, alone, have been dealt with. Mention might have been made of the isolated hill-top pockets of podocarp forest stranded in a maze of mountain and silver beech forest types to the north of the Lillburn Valley, of the hill podocarp stands developed on cold aspect slopes at the head of the Waikoau Valley, of the stagnant kahikatea/silver beech stands on the eastern shore of Lake Poteriteri, and so on. These items, and many others, will be described when final reports on these forests are compiled from Forest Survey Records. For the moment the intention has been to leave no more than a general impression that, in these forests, there exists a most intricate and kaleidoscopic confusion of various forest types, a confusion which can, nevertheless, be brought to order through use of the hypothesis of recent climatic change.
The forests of the south-west vary in composition, in quality, in vigour, in management potential and in type origin almost from acre to acre; and this jigsaw puzzle appeared, at first sight, incapable of resolution. But, by means of one basic working hypothesis, even the most anomalous features proved susceptible of ready resolution. That, of itself, might be considered strong presumptive evidence of the validity of the hypothesis but this evidence does not stand alone. The present condition of the south-western forests can be related to conditions as they obtain in other South Island forests. Before this relationship is discussed, however, it will be best to take, by way of introduction, one further problem item from the present area.
Mention has already been made of the relict pockets of matai forest in the Longwood Range, and of the isolated matai on the highest hill crests in the Alton-Rowallan area. Mention might have been made of the single veteran matai
located on the lower flood plain of the Waitutu River, the only matai found in the forests to the west of the Hump Ridge. Further isolated specimens occur along the Waikoau River and immediately to the east of Lake Hauroko. Straggling stunted specimens are also found at an altitude of 2,000 ft. on the escarpment cliffs of Helmet Hill.
Without exception these randomly distributed trees are all old and defective or, if younger, stunted and malformed. Their random distribution could be attributed to occasional establishment following bird distribution of seed but this explanation in no way accounts for the age and general condition of the trees. The most likely explanation is that, in these forests, matai is a true relict species in rapid course of complete extinction. This interpretation is in line with Cockayne's evidence (loc. cit. p. 166) from the forests of Stewart Island where living matai occur rarely though there is a frequent abundance of long dead, fallen, matai logs.
Confirmatory evidence is derived through study of certain forest types to the north of the Lillburn Valley. Here, on dry sandstone and siltstone ridges, occasional very old matai may be found on the ridge crests within stands of young and vigorous mountain beech. Scattered through these stands, also, are a few old defective silver beech but frequently this species is represented by stump and log mounds only. The age of the veteran matai is estimated, conservatively, at upwards of 700 to 900 years, growth rates being so slow that ring counts, in the field, could only be made with the greatest difficulty. The living silver beech are, at most, some 300 to 400 years of age, log and stump remains of this species, on these sites, normally disintegrating within 50 years. The dominant mountain beech are all young trees. A few may reach an age of 200 years but most are less than 120 to 150 years old.
The only tenable explanation is that, at some date less than 1,000 years ago, a type of forest in which matai was well represented flourished on these ridges. This matai containing type was later replaced by a type in which silver beech was the dominant species and silver beech, in its turn, has recently been replaced by mountain beech. The full immigration pattern for mountain beech can still be traced though the silver beech patterns have been lost with the effluxion of time. In this area a position of relative stability, under present climatic conditions, would appear to be reached when mountain beech has completely occupied the ridge crests and all slopes of dry aspect, silver beech remaining dominant on moist shady slopes and in gullies. The logical conclusion must be that there has been a progressive drying out of the forest accompanied, perhaps, by a fall in temperature, a change adverse to matai and its associate species and favouring, first, silver beech and, finally, the xerophytic mountain beech. And a few long living survivors from the ancient forest outlast all changes but are incapable of self reproduction.
This ability of matai to survive under adverse climatic conditions coupled with its extreme longevity renders it a species of great value in the study of forest distribution patterns as affected by changing climates. Matai, in respect to its ability to regenerate, would appear to be one of the first of all forest tree species to be affected by climatic changes in direction away from its optimum but, as already pointed out, through its capacity for survival it remains in the new forests as a living monument to the old climates.
The Matai Forests, Past And Present
The distribution, in the South Island to the east of the main divide, of podocarp forests in which matai, together with true totara, kahikatea and, occasionally, rimu are the physiognomic species presents many most peculiar features. Such forests are never of any considerable extent but they occur widely distributed from Bluff northwards to the Marlborough Sounds, discontinuous small pockets of forest surrounded by tussock grasslands, manuka scrublands or, more rarely, by beech forests of varying type. And underlying this gross discontinuity there can be traced no uniform factor of climate or of soil. Forests of this type occur in the swamps and on dry wind exposed hillsides, near the coast and inland along the foothills of the Southern Alps, in frost free localities and in districts where heavy winter frosts and snows are normal. They are found on limestones and on other sedimentary rocks, on greywackes, schists, volcanics and on recent alluviums. In most cases the forest soils are, agriculturally speaking, very fertile soils but this would generally appear to be more an effect than a cause, an outcome of soil fertility building by matai and its associate species than a factor to be invoked in explanation of distributional abnormalities. One other feature, only, is common to all these forests, the over-maturity or senescence of the physiognomic dominants with an almost complete absence of young, healthy, vigorous growing stock.
Many of these small forests have been destroyed completely by axe and by fire to give place to productive farmland. Some may have disappeared without trace or record, but, at their maximum extent as known by Europeans, these introductory remarks applied. The relict character of these forests, their pocket handkerchief size, their discontinuous distribution, has been but emphasised by post-settlement activities. Study of them might begin by linking them with the forest remains, logs and charred wood fragments, found by pioneer settlers liberally distributed throughout the tussock grasslands from the Canterbury Downs through the MacKenzie Country to the semi-arid inland basins of Central Otago, from sea-level to mountain summits (Speight loc. cit.), but it might be better to begin once more in Western Southland.
The Waiau Valley Matai Forests
Motu Bush (see Locality Map No. 2) is an isolated block of forest lying on the west bank of the Waiau River a few miles to the east of the sandstone ridge matai/silver beech/mountain beech stands described in the concluding section of Part I of this report. It is, in respect to its southern portion, a silver beech/mountain beech/rimu forest and a silver beech/rimu forest to the north. On the alluvial river terraces along the eastern margin there is a considerable admixture of forest types with local pockets of kahikatea swamp forest interspersed through mixed stands of silver beech, mountain beech, matai, kahikatea, rimu and hybrid totara. These mixed stands occupy soils of markedly greater fertility than the hill soils, derived from siltstones, of the bulk of the forest and to this factor might be ascribed the presence of matai, kahikatea and totara. But in one area on the hill slopes there are a few hundred acres of matai/totara/kahikatea stands and these occupy soils of identical geological origin to those of the surrounding beech stands. In these hill podocarp stands the dominant matai, totara and kahikatea are very large trees with massive boles and immense
spreading canopies. They stand, widely spaced apart, over a low, floristically rich, dense shrubbery in which broadleaf (Griselinia littoralis) and fuchsia (Fuchsia excorticata) play a conspicuous part. There are no young podocarps present nor is there any trace of persistent podocarp regeneration. In chance forest clearings cabbage trees (Cordyline australis) and kowhai, neither being characteristic species of a forest interior, become established.
A similar type of forest is found on the lower slopes of the Longwood Range at the northern end of the range, near Merrivale. Here the shrub tier is even denser and floristically richer while the podocarps, massive matai, kahikatea and rimu are even more widely spaced apart; and somewhat higher on the hill slopes the only living true totara discovered in the Longwood Range are located. Few stands of this type still remain intact. The sites have largely been cleared for settlement. But from Merrivale south around the western foothills of the Longwood Range occasional matai may still be found in the valleys with local ridge top stands of the Merrivale or Motu Bush types.
These stands are further characterised by local abundance of the following associate species, pigeon-wood (Hedycarya arborea), kaikomako (Pennantia corymbosa), milk-tree (Paratrophis microphylla), lowland ribbon wood (Plagianthus betulinus), Melicope simplex, and Myrtus obcordata; and all these species, in the far south, rarely occur save in association with matai. In these areas, also, the vine Parsonsia heterophylla. achieves a luxuriance rare elsewhere. The common ground fern in the forests of the south-west as a whole is the tuft fern Blechnum discolor, locally replaced in certain types of rimu forest by Blechnum capense but the common tuft fern in the matai stands is Polystichum vestitum with local abundance of Dryopteris pennigera, the latter restricted to matai sites. Other species may also be linked to matai. Thus mahoe (Melicytus ramiflorus) seldom occurs, away from coastal forest, except in association with matai. Broadleaf and fuchsia always occur in abundance in the matai stands and both cabbage trees and kowhai are found plentifully in forest clearings and around the forest margin. These species are mentioned here since, as will appear later, they frequently possess an indicator value.
To the north-east of the Merrivale matai stands the forest known as Island Bush was, prior to logging, almost entirely a matai/totara/rimu/kahikatea forest generally similar to the Motu Bush type though with a strong representation of rata and kamahi. Both to the north and to the south of Island Bush silver beech stands are developed on higher ground (Longwoods and Woodlaw) but Island Bush itself has been effectively shielded from invasion by silver beech by the topographical low points, Scott's Gap and Raymond's Gap. Invasion could only proceed uphill from the Gaps or from even lower ground to the east and west; and silver beech is present on the lower slopes in an almost complete fringe around the hill matai stands. On these lower slopes silver beech is vigorous and aggressive but it penetrates the heavy secondary scrub characteristic of the matai areas only with the very greatest difficulty.
To the north of Island Bush, Woodlaw Forest is, in respect to its eastern portion, largely a silver beech forest with scattered rimu, kahikatea, miro and Hall's totara on the hill slopes and local kahikatea stands on the lower swampy ground. Matai occur rarely, rata is not represented and kamahi, normally widespread in forests of this type, occurs only in shrub form in one or two gullies. Following logging operations, the kahikatea in the swamps regenerate freely but
the hill podocarps do not regenerate and are replaced by silver beech. On many sites conditions appear more suited to mountain beech than to silver but only a single tree of this species has been found in the forest. This is located in the bottom of a deep gully which heads back to the lowest point on the watershed separating East Woodlaw from a potential mountain beech seed source, the Orauea River. But the intervening forests have been cleared to farm so that, at this date, it would be impossible to determine whether the Woodlaw mountain beech specimen is a recent entrant into the forest or a riparian site survivor from some forest period preceding the podocarp forest era.
In sharp contradistinction to East Woodlaw the western portions of Woodlaw Forest are entirely derelict degenerate matai stands. Here, on steep slopes of warm aspect, the physiognomic species is broadleaf and, throughout the broadleaf stands, a few gnarled ancient matai survivors persist. And any list of secondary species would include most of those listed as characteristic matai associates.
Closely comparable scrub broadleaf forest (with much fuchsia) is widely developed some ten miles or more to the north of Woodlaw on the south-western slopes of the Takitimu Mts. These areas of scrub forest have not been closely searched for relict matai but this type of scrub forest is identical in composition with that known to develop in many areas following the gradual elimination of matai. This scrub type may, therefore, justifiably it is believed, be regarded as representative of matai forest in the final stages of extinction.
Small pockets of broadleaf, occasionally in association with silver beech or, to the north, with mountain beech extend around the western slopes of the Takitimu Range. Typically they occupy, in part, the deeper colluvial soils subject to ground water seepage along the toe of the main mountain slopes but they also occur, sporadically, on the steep rocky slopes above. Floristically they bear a close resemblance to the West Woodlaw broadleaf/matai stands. Thus there is commonly a heavy floor cover of Polystichum vestitum with local abundance of Dryopteris pennigera. Parsonsia heterophylla grows luxuriantly and Melicope simplex and Myrtus obcordata together with lowland ribbonwood are frequent associate species. No matai can be found in this area to-day but local reports state that a few trees, long since felled, were present several decades ago.
As these broadleaf stands open up, both cabbage trees and kowhai enter in as in the case of the Motu Bush stands. Later, and to the north, the broadleaf in turn thin out and disappear leaving the kowhai and cabbage trees dominant and, finally, these two species alone remain. Groups of cabbage trees and kowhai, separately or in association, occur on broad rolling ridges falling from the Takitimu Mts. to Lake Monowai. In such localities tufts of Polystichum vestitum may occur amongst the tussock grasses in the damper hollows and occasional broadleaf are found in the deeper gullies. Broadleaf/totara stands still exist in several of the deep mountain valleys in the north-west quarter of the Takitimu Mts. The totara is mainly stunted Hall's totara but, in many instances, the larger trees possess characteristics of leaf and bark more typical of true totara and hybrid origin is suspected. Matai appear again, many miles to the north, as isolated trees scattered through red beech/silver beech/mountain beech forests to the east of Lake Te Anau.
But to turn southwards again, down the Waiau River back to Motu Bush: a few stunted matai are found in silver beech/mountain beech forest at Blackmount near the confluence of the Waiau and Monowai Rivers. In Taylor's Bush, a little to the south of Blackmount, matai, totara and kahikatea occur in association with riparian silver and mountain beech on warm limestone slopes and on deep river silts subject to lime rich drainage. All the noted matai associate species, save milk-tree, are present as is also Helichrysum glomeratum, a frequent matai associate on lime rich soils.
On the hill slopes adjacent to Taylor's Bush cabbage trees and kowhai occur in groves dotted through the short tussock grassland and a few such groves occur within the Bush itself. In Taylor's Bush, also, some seedling and sapling matai are present with occasional small groups of matai poles, a feature noted in no other forest in Western Southland. This would appear to be the result of exceptionally favourable local conditions, deep fertile soils, warm aspect, shelter from winds, and rapid down river drainage of cold air. The local site on which the young matai occur is relatively frost free.
South from Taylor's Bush remnant pockets of hill slope matai/kahikatea/totara forest are found on Bell Mount and on adjacent hills. They are generally similar in type to the Motu Bush stand though the forest understories have been considerably modified by animal grazing. The stands normally lie on the moister, though colder, slopes and occur with greater frequency on limestone outcrops than on any other strata. In certain cases, rata and kamahi enter the stands which are then more akin to those of Island Bush than to the Motu Bush type; but the precise factors controlling the distribution of these two species in forests of this broad type have not yet been studied. These isolated pockets of forest away from the Waiau River generally contain no mountain or silver beech. They are separated, one from another, by tussock grasslands and manuka scrublands through both of which kowhai and cabbage trees are widely distributed.
Further typical relict matai/totara/kahikatea stands occur on Diggers Hill to the west of the Waiau River with extensive broadleaf/fuchsia/kowhai/cabbage tree scrub forest stands developed on steep slopes of warm aspect. Above these Diggers Hill matai stands there are pure stands of silver beech; below them, on river terraces along the Waiau River, very mixed stands containing both silver and mountain beech together with stunted matai, veteran true totara, Hall's totara, hybrid totara, kahikatea, miro and rimu are developed. Mountain beech is the normal dominant near the river margin with silver beech dominant toward the hill. At the base of the main hill slopes extensive swamps carry heavy stands of kahikatea, all trees being of considerably younger age than the veteran kahikatea in the hill stands. The pure hill-type matai/totara/kahikatea stands, in this area, are found only on the Diggers Hill limestones but, on adjacent sandstones, mountain beech/silver beech stands contain a few very large matai and kahikatea.
Several distinct types of relict matai forest have already been enumerated. Others might be added. Thus, to the east of Motu Bush and across the Waiau River, randomly distributed pockets of forest occur on a local gravel plain. These pockets are now surrounded by cultivated farmlands but this farmland formerly carried tussock grassland and manuka heath. The largest of these pockets of forest, Lonneker's Bush, is a matai/totara forest. Both true totara
and Hall's totara, with many hybrids, are present together with small excessively misshapen matai. One or two silver beech trees are present and these lie in such a position that they could have entered the stands from a Waiau River tributary stream to the north, Takitimu derived seed. The hill and terrace slopes to the east carry stands closer to the Island Bush stands in type but the typical Lonneker's Bush type is the mixed totara/stunted matai type of the stony gravelly silt soils of the plainland. And where forest of this type has been destroyed exposing the fine fertile silts to wind erosion, manuka heath develops.
Other pockets of forest on this local plain are generally similar in composition though, wherever they lie close to the Waiau River, mountain and silver beech enter the stands; and where soils are moister than usual kahikatea is also present. Some of these pockets of forest are now in the final stages of destruction. Where this is the case a most characteristic feature is the rapid invasion of the sites by the exotic elderberry (Sambucus nigra) and, in one instance at least, thickets of elderberry alone remain as evidence of the one-time presence of matai forest.
Between Lonneker's Bush and West Woodlaw matai containing forest remnants occur at Eastern Bush. More extensive stands were once widely developed on the Clifden limestones; and the Feldwick limestones, lying between Eastern Bush and West Woodlaw, carry pockets of scrub forest containing many matai associate species. To the south, matai occurs in several mountain beech/silver beech stands developed along the flood plain of the Waiau River, extending from Motu Bush almost to Tuatapere.
Now all these matai containing stands, as shown on the map, lie within a well defined valley region. They are not separated, one from another, by any major areas of forest of any other type but by tussock grasslands and scrublands only Mountain and silver beech enter the stands only around the periphery of the matai region and along stream and river courses. On this evidence alone it might safely be argued that these stands are relict stands, remnants of once more extensive forests; and this hypothesis sufficiently explains the present condition of the stands and the behaviour therein of the physiognomic podocarps. There are, however, other lines of evidence to the same end, evidence which might be presented before further discussion of these Waiau Valley matai forests.
The Ancient Waiau Valley Forest
The Waiau Valley tussock grasslands have, for close on a century, carried large flocks of sheep but it has only been within recent years that the pattern of land-use has tended to become more intensive with replacement of indigenous grasses by exotic grasses and provision of supplementary feed. This has entailed the drainage of local swamps and these drainage operations, in many cases, have been rendered difficult on account of immense quantities of swamp buried timber. These buried logs, unmistakably of matai and kahikatea, do not appear to be of very great age. The bark is usually intact and the exhumed logs are commonly used for fuel.
Superimposed on the patchwork of existing forest we have, therefore, a patchwork pattern of buried swamp forest. This still leaves considerable areas over which no trace of a former forest cover is discoverable; but locally the soil surface of these apparently natural grasslands is perceptibly dimpled and this dimpling, elsewhere, is a characteristic feature of grassland won from forest. In yet
Photo 1—(Photo ref 1243/36) Ridge [ unclear: ] podocarp Stands, Rowallan River watershed Western Southland R [ unclear: ] mu stands, [ unclear: ] and kamahi sub-dominant. Occupy the crest of the interfluve. The hill slopes, carry sliver beech/ [ unclear: ] stands with the latter species steadily increasing in abundance with gain in altitude Mountain beech, indistinguishable from Silver beech in the photo, occur only toward the valley floors (Refer to text p. 341)
Photo 2—(Photo ref 1246/37) Coastal fluvro [ unclear: ] -glacial gravel t [ unclear: ] e podocarp stands Waikoau River Western Southland Heavily stocked [ unclear: ] ni stands (outlined) occupy the main portion of the gravel te [ unclear: ] e but silver beech has n [ unclear: ] vaded the stand around its ent [ unclear: ] e landward [ unclear: ] and perimeter and down all the streams traversing the [ unclear: ] Mountain beech occurs on [ unclear: ] pa [ unclear: ] n sites and mixed mountain beech/silver beech stands occupy the [ unclear: ] wise slump [ unclear: ] s when mudstones are exposed (Refer to text p. 351)
Photo 3—(Photo ref 1248/65) sliver beech migration patterns Longwood Range Southland [ unclear: ] Silver beech pole Stands (dark even [ unclear: ] ) etend down all Streams draining an isolated ridge [ unclear: ] Marked) on which [ unclear: ] an open silver beech/ [ unclear: ] stand. The [ unclear: ] forest mass consists of [ unclear: ] (pa [ unclear: ] logged) with heavy [ unclear: ] ta and kamahi No sliver beech are found along any Streams other than those having then source near the ridge crest silver beech stand (Refer to text p. 345).
Photo 4.—(Photo ref.: 1244/32). Limestone soils a barrier to migration of mountain beech. Helmet Hill, Western Southland. carries open stands of silver beech and kamahi on the dip slopes and silver beech/rimu/kamahi stands on the escarpment slopes. On siltstones to the east and on mountain beech/silver beech/rimu stands and mountain beech/silver beech/kahikatea stands. Relict matai (single trees) occur to an altitude of 2,000ft. (points marked X). In the extreme south, silver beech has invaded coastal gravel terrace rimu stands. Mountain beech has nowhere crossed the line of limestone outerop save on the driest escarpment slopes to the north. (Refer to text p. 346.)
Photo: Crown copyright. Lands and Survery Department.
Photo 5.—(Photo ref.: 1238/49). Reliet hill matai/totara/kahikatea stand, Motu Bush, Western Southland. A very open stand of large veteran matai, kahikatea and totara (outlined) forms an encleave within a forest now wholly of silver beech and mountain beech with widely spaced old rimu. No seedling, sapling or pole podocarps occur within the matai stand but there is peripheral eneroachment by the beech speeles. The forest boundary to the south is a typical ‘fire induced’ boundary suspected of being, in part at least, of pre-European origin. Where the forest has recovered after these fires mountain beech is the universal dominant. It is aggressive species over the greater part of the whole forest. (Refer to text p. 355)
Photo: Crown copyright. Lands and Survey Department.
Photo 6.—(Photo ref.: 1244/60). Overmature matai/kahikatea/rimu stand. Longwood Range. Southland. In this are near Merrivale at the northern end of the Longwood Range the lower slopes (A) carry very open stands of large diameter, defective podocarps which, as evident in the photograph, stand out above a low, dense underwood of scrub hardwood species. Over wide areas there are not more than two or three surviving podocarps per acre. No young podocarps are present. The underwood is floristically very rich. as is usual on old matai sites; 25 separate shrub species have been recorded on a single 1/80th acre quadrat. On the upper slopes of the Range (B) the relict podocarp stand merges into a silver beech stand containing widely spaced large rimu. A few true totara, the only living specimens found in the forests of the Long wood Range, occur at approximately the position marked (T). Refer to text p. 357.)
Photo: Crown copyright. Lands and Survey Department.
Photo 7.—(Photo ref.: 1477/5). Zonation of stands around open pakihi, Okuru River, South Westland. Forest type distribution patterns such as these are typical of the Westland coastal plains. Around the margins of the pakihgi there are in evidence all stages in the succession from pakihi through manuka scrub to silver pine to rimu high forest. Islands of forest of varying age also occure withing the pakihi on local dry sites. The oldest stands, rimu/rata/kamahi, are found only on well drained sites, e.g., on the hill slopes, on terrace margins. and on well drained recent alluvial soils. Kahikatea and occasional matai occure in association with the rimu on the alluviums and dense kahikatea pole stands form on alluvial soils where these are swampy. In the present instance, also, some silver beech is hound in the stands near the main streams, extensive silver beech forests ovvuring on the mountains a few miles to the east. The stands on the alluviums near the main river have been partly cleared to pasture.
Photo 8.—(Photo ref.: 1536/6). Rimu forest of the eoastal plains, Saltwater, Westland. The patehy mottled texture of the stands will be radily apparent. This reflects the strongly group even-aged eondition of the forest and this, in turn, is considered indicative of the origin of the stands—i.e., through progressive eolonisation, by rimu, of pre-existent pakihi. Reliet Silver pine or, more rarely, old stems of manuka, occur within the youngest rimu stands (even-textured light grey pockets). Old rimu occur seattered through heavy stands of rata and kamahi on dry morainie ridges and on other well drained sites along the main streams. (Refer to text p. 380.)
Note.—All photographs from an altitude of approximately 12,300ft., within a camera of focal length 8¼ inches to give an approximate photo scale of 4 inches to 1 mile. Reduced to approximately 3 inches to 1 mile on reproduction.
Photo: crown copyright. Lands and Survey Department.
other localities where the natural vegetation would appear to be manuka heath, the heath soils do not, to the eye, differ significantly from the soils of the Lonneker's Bush totara/stunted matai forest type, assuming loss of topsoils through wind erosion. It might be stressed here, however, that the greater part of existing manuka heath is excluded from this category. It is considered to be induced heath and its origin will be further discussed below.
On the basis of all evidence to hand, the history of the vegetation of the Waiau Valley might be outlined as follows.
At some comparatively recent date podocarp forests characterised by the frequent dominance of matai occupied the valley lowlands from Merrivale, in the south, to Lake Manapouri in the north, from West Woodlaw and Island Bush in the east to Motu Bush in the west. Outlying stands were developed well to the north, west and south of these limits within the then rimu forests of coastal districts and within rimu/beech forests near Lake Te Anau; and the Waiau Valley matai forests were linked, through Island Bush, with extensive matai/totara/kahikatea forests developed on the Southland Plains.
Consequent on some regional climatic change these matai forests then entered into a long period of stagnation and decline. There was no longer any effective regeneration of the physiognomic dominants, particularly, at first, on the poorer sites and soils, and all subsequent growth of trees already established was poor, leaving the residual stands with an excessive proportion of stunted, defective or malformed stems. As the stands opened up through death, decay and windfall, the former secondary species of the forest understories, characteristically broad-leaf and fuchsia, assumed dominance though wherever a seed source was available silver beech and mountain beech invaded the stands. This could only happen, and has only happened on high ground or on riparian sites near streams and rivers draining from high ground. As conditions became more markedly adverse the secondary scrub forests, in turn, opened up and died out in patches with incoming of such atypical forest species as cabbage trees and kowhai, and with local development of pockets of grassland within the main forest mass. The final result has been the development of a mosaic of forest and grassland with some manuka heath developed on the poorest or eroded soils. The remnant pockets of forest are restricted, in general, to the deeper, moister and more fertile soils and each and every remnant pocket is distinct in composition and in condition reflecting all the many local site type differences evident in the ancient forest and reflecting all possible stages in forest stagnation and decline.
Kahikatea, in contrast to matai or, more accurately, to a greater extent that matai, survived through facultative adaption to swamp forest conditions; but all the very old and very large kahikatea are to be found in the derelict hill forest stands in association with matai. During the period of the matai forest climatic optimum kahikatea was mainly a species of the hill slopes, not a typical swamp tree as it is to-day. True totara, like matai, possessed no such plasticity and, over the greater part of its former range, has died out, occasionally leaving, as evidence of its one time presence, fallen logs of durable heartwood; or, in other instances, it has lost its identity in hybrid swarms with Hall's totara, a species far better adapted to the new climates.
The final decay and breaking up of the forest was undoubtedly accelerated by fire. Thus, at an altitude of 3,000 ft. on the western slopes of the Takitimu Mts.,
and in the midst of a waste of rock rubble, scree and bed-rock gullies, the soil under a remnant patch of tussock grassland showed ten inches of a dark, crumb structured grassland soil over two inches of fine, slightly weathered rock fragments which overlay, in turn, a shallow bed of charcoals. Below the charcoals there was a truncated fossil soil, strongly leached with traces of iron pan and marked root channels. The climate must, at one time, have been such as to support forest growth on these exposed high altitude sites. This forest was destroyed by fire, presumably following deterioration in the climate and when the forest was no longer in a condition to re-establish. Following the fire the site was occupied, after a short period of accelerated erosion, by tussock grassland which persisted for a sufficiently long period of time for formation of an appreciable depth of true grassland soil on top of the charcoals and erosion detritus until destroyed, in turn, on initiation of the present erosion cycle. To-day, in respect to this particular site, the climate would appear too severe to permit re-establishment of any type of indigenous forest. It is possibly too severe to permit even the re-establishment of indigenous tussock grassland.
At lower altitudes, in the same general locality, over-grazing or over-burning of the tussock grassland leads to invasion of the pasture by manuka heath. On these sites the climate would seem, to-day, to be favourable to the development of mountain beech forest and, where this is so, the invasion of the damaged grassland by manuka might be interpreted as a first stage in the development of beech forest, a development which has been long delayed by the entrenched sub-climax tussock grassland which occupied the site following disintegration of the original matai forest and in the absence of a beech seed source.
In one instance, at least, the pre-European fires spread beyond the limits of the stagnating podocarp forest and burnt back the advancing beech forest. Some ten miles to the west of the charcoal bed described above, pioneer type, branchy “forest edge” trees were discovered at a distance approximately half a mile within the present forest margin. And, once again, charcoals were found in the subsoil. Judging from the age of these pioneer type silver beech and mountain beech, and from the age of the young stands lying between them and the forest edge, this fire occurred somewhere between 300 and 400 years ago, i.e., two to three centuries before European occupation of the country. Other fires have been dated, by ring counts on fire scarred trees, to 200, 150 and 120 years ago.
The Polynesians, Moa-hunter and Maori, were in occupation of the land for a period of at least 800 years prior to the advent of the European settler (Duff, 1950). They used fire but had no effective means of controlling fire and existing forests carry the mark of these ancient fires to this day; but, in so far as can be estimated, the ancient matai forests of the Waiau Valley must already have entered their period of decline and were probably in an early phase leading to the development of a mosiac of grassland and forest when Moa-hunter culture was at its peak. Man was an agent in forest destruction but the primary cause lay in forest instability. The Polynesians played little part in shaping the forests of high rainfall regions but the relict matai forests and beech forests of low rainfall regions to the east of the Southern Alps bear the imprint of a long period of cultural interference.
The present conditions of the Waiau Valley matai forest is, therefore, readily explicable in terms of that same basic hypothesis evoked in explanation of the
abnormalities displayed by other forests in Western Southland. The climatic changes which lead to the invasion of the coastal terrace bog forests by rimu, to the invasion of the rimu forests by silver beech, and to the invasion of the silver beech forests by mountain beech, lead also to the stagnation and desiccation of the matai forests, to their partial replacement by tussock grassland and manuka heath, and laid them open to destruction by fire. On the pragmatically sound principle of minimum complexity this might well be considered strong grounds for a firmer belief in the validity of the basic hypothesis.
But before abandoning the topic of the ancient Waiau Valley matai forests, two further related items might be mentioned.
Reference has already been made to red beech (Nothofagus fusca) as a species found in association with veteran matai in the forests to the east of Lake Te Anau. Throughout the mountain forests from Te Anau northwards red beech is a frequent forest dominant. To the south of Te Anau it occurs in lesser amounts near Lake Manapouri and in several of the north draining valleys of the Takitimu Mts. In none of these latter localities does red beech appear vigorous and, following any gross disturbance of the forest canopy, it is rapidly displaced by mountain beech or, on certain sites, by silver beech. In other words, it behaves in these stands as a species at the extreme limits of its climatic range; but there is, nevertheless, evidence to show that, in the past, these limits exended very much further to the south.
Near Lake Monowai two separate half-acre pockets of rather unhealthy appearing red beech have been found within silver beech/mountain beech stands; and, well to the south again, a single group of three trees have been found in silver beech/mountain beech forest in the valley of the Bryce Burn, a tributary of the Lillburn. All three of these red beech pockets lie in such a position away from streams draining major areas of red beech forest that they can only be considered true relics. And this supposition is strengthened by the discovery, in several separate localities to the south of Lake Monowai, of undoubted red beech × mountain beech hybrids remote from any possible red beech parent trees.
It would appear probable, therefore, that the period which saw the matai forests fully developed was also a period during which red beech extended well to the south, almost to Foveaux Strait. Since that time its range has contracted northwards leaving remnant pockets such as those in the Bryce Burn and near Lake Monowai, the last survivors, in many other instances, having been swamped out in hybrid swarms with mountain beech. The distributional peculiarities of red beech in the forests of the far south, and its behaviour in the southernmost red beech dominant stands, are explicable only in terms of regional climatic deterioration unfavourable to this species.
Finally, some brief mention should be made of the peculiar scrub forest, known as “The Wilderness,” which lies surrounded by tussock grassland and manuka heath to the east of Lake Manapouri. This scrub forest with bog pine the physiognomic species appears in every way closely related to true bog forest as developed on wet ground in districts with rainfall treble that experienced to the east of Manapouri. Its development in a district with a low actual and effective rainfall has long been puzzling; but if it be regarded as a relict bog forest surviving from the wetter matai forest era then its occurrence is understandable. Many minor types of forest must have been contained within the ancient matai
forests which would have been no more uniform in composition than are, for example, those Central North Island forests characterised, to-day, by the frequent dominance of matai. And all these minor forest types, to a greater or lesser degree, will have left some impress on the soils and on the present vegegation.
The Matai-Forests Of Canterbury And Otago
The inland and eastern regions of Canterbury and Otago are commonly regarded as the great natural grassland regions of New Zealand. This was their predominant character at the date of European colonisation, tussock grasslands lying in the rain shadows thrown by the main mountain ranges and bordered by the beech forests of the foothills. But throughout the entire region from the Waiau Valley northwards to the Wairau Valley in Marlborough there occurred (and still occur) discontinuously distributed pocket handkerchief podocarp forests of the types described above.
The Waiau Valley forests were, as already noted, inter-connected with the matai/totara/kahikatea forests of the Southland Plain through Island Bush. On the Plain there was an intricate mosaic pattern of forest, grassland, scrubland and swamp with more extensive podocarp forests developed on the Hokonui and Forest Hills and on the hill country to the east of the Mataura River. These latter stands adjoined the rimu dominant coastal climate forests of the Catlins region but matai type stands reached the coast to the north of the Clutha River and, from this point northwards, occupied a narrow coastal zone finally disappearing, where in turn the tussock grasslands reached the coast, near Oamaru. Inland, matai stands were to be found near Clinton, near Tapanui, and to the west of the Taieri Plain.
In South Canterbury similar forests existed in the Hunters Hills to the west of Waimate and in the gullies and folds of the South Canterbury Downs from Waimate to Temuka and Geraldine. They were more widely developed on Mt. Peel and on Banks Peninsula, vide infra, with lesser stands on the Canterbury Plains themselves, e.g., Riccarton Bush and Papanui Bush (Christchurch) and at Woodend. Small stands were found throughout the coastal hill country of North Canterbury with more extensive forests developed on the seaward slopes of the Kaikoura Range from the Conway River north to the Wairau.
Inland, matai containing stands occupied portion of the Grey Downs and formed the bulk of the old Harewood Forest adjoining the present hill country beech forests of Mt. Oxford. They occurred, also, at Kowhai Bush near Springfield and in Alford Forest to the west of Methven. South from this point there is an apparent gap until the matai/totara/kahikatea stands of the lower reaches of he Makarora Valley are reached and there is a further gap southwards to Lake Te Anau and the Waiau Valley.
But many of these gaps can be filled, if not with existing matai stands then at least with traces of such stands. The gap from Springfield to Alford Forest is filled by a single veteran matai recently discovered in the mountain beech forest on Mt. Algidus. Near Lake Hawea no living matai can be found but matai stumps with pit-sawyers trenches dug alongside have been found; and to the west of Mt. Peel, bordering the semi-arid grasslands of the MacKenzie Country, a single totara (probably Hall's totara) still stands in a high gully on Mount Fox. In all probability many small pockets of forest have been destroyed without record.
Thus in the gap between Springfield and the Rakaia Gorge prolific growth of the exotic elderberry as an understory to a plantation of exotic conifers lead to the making of local enquiries and to the dim recollections of an elderly ploughman who thought that the plantation was sited on ground where buried stumps gave trouble during the early breaking in of the tussock grasslands; and buried logs have since been found on many sites in the same general locality.
Broadleaf scrub forest containing many species which, as shown for the Waiau Valley matai stands, are characteristic matai associate species, is found in many places. The best known of these scrub stands is possibly that in the Ashley Gorge but smaller stands are found on a wide variety of sites, e.g., near the confluence of the Boyle and Lewis Rivers in the Lewis Pass region and in the upper reaches of the Rakaia and Rangitata rivers. These latter occurrences will be described in greater detail below.
Existing matai stands, as in the case of the Waiau Valley matai forests, are also linked by the fallen logs formerly discoverable in vast quantities throughout the tussock grasslands. Speight (loc. cit.) has gathered together much of the detail of these discoveries, information which has recently been recapitulated and amplified by Raeside (loc. cit.). The logs, generally stated to have been of totara, were found at Cheviot in North Canterbury and throughout the hill country between the Waipara and Hurunui Rivers; they were found at Amberley and on the Malvern Hills, on the downs to the west of Timaru and in the MacKenzie Country; Burnett (1926) noted them at 4,000 ft. on the Tasman Downs and Raeside records them from 4,000 ft. on the Kirkliston Range; they were found over wide areas in the Rakaia Valley and on the Arrowsmith Range. There are many references to their former abundance in the Central Otago region. Park (1908) noted them from above 2,000 ft. on the Dunstan, Pisa, Remarkable and Carrick Ranges and they may still be found in the Nevis Valley which is now treeless, parched and arid in summer and subject to intense cold with three to four months snow cover each winter. In this valley the European gold-miners split for mining timber the totara logs found high on the mountain sides and in the same valley the forerunners of the gold-miners, the Maoris or Moa-hunters, utilised immense quantities of wood for fuel. Extensive charcoal beds containing stone chippings and bone fragments have been found and this fuel wood must have been gathered in the near locality.
There are likewise many references to the use of these totara logs for fencing timber. Their soundness and fresh appearance was the subject of frequent comment. One report states that logs have been hauled down from the upper slopes of the Pisa Range for conversion into window frame and other joinery timber (Field, pers. comm.).
In Canterbury, Speight found evidence suggesting that the old Harewood Forest once extended down across the plains to link, almost, with the forest between Woodend and Kaiapoi and that this latter forest extended from Amberley through Woodend and Marshland to Christchurch itself. Swamp or semi-swamp forest stretched from Christchurch through Tai Tapu to Ellesmere and Rakaia Mouth with additional extensive forests at Longbeach between Ashburton and the sea. To the south, forests once extended from Orari Mouth almost to Timaru. These swamp forests have been identified as kahikatea/matai forests. Inland, the ancient forests of the hills and downs have usually been named totara forests
but this is probably only because, of all the species once represented, only the totara possessed sufficient natural durability to outlast the period in between the destruction of the forests and the advent of European settlers. Totara must certainly have been dominant on certain sites as it is on certain sites in existing forests but, on other sites, matai, kahikatea and possibly rimu would all have shared dominance. Broadleaf and Myrtus and other typical associate hardwoods have likewise been identified while rata logs may yet be found in the Lake Coleridge area; isolated rata trees still grew around the lake shores in the early years of settlement (Barker, 1950, p. 117). All present indications are that the forests were, essentially, closely comparable with the inland matai/totara/kahikatea/rimu forests of the North Island as these exist to-day.
For South Canterbury, Raeside (loc. cit.) has demonstrated that the downland soils are not, as might normally have been expected, tussock grassland soils though tussock grassland appeared to be the natural vegetation of the downs. The soils are, in fact, somewhat modified forest soils and the conclusion that the downs were, comparatively recently, entirely forested is inescapable.
So far, in this discussion, nothing radically new has been added to our knowledge of these ancient forests. Speight fully appreciated the fact that regional climates must have undergone some significant change and Raeside emphasised the point that this change must have been of comparatively recent date. It remains but to relate these facts to the present condition and behaviour of existing forests and, for this purpose, certain Canterbury forests must be considered in greater detail.
The Forests Of Banks Peninsula, Mt. Peel And The Upper Rakaia
It will already have been realised from the account given in the preceding section of this report that the remnant matai containing forests of Otago and Canterbury merely reproduce on a more considerable scale all the many peculiarities of distribution and of type already noted for the Waiau Valley stands. The Waiau Valley region is but the whole in miniature. Throughout, there are the same marked variations between one pocket forest and the next with respect to species admixtures and to the form and condition of the forest dominants; and, throughout, there is the same marked preponderance of old veteran trees in the stands.
According to Cockayne (loc. cit. p. 174), “On Banks Peninsula and in certain other places where sapling tall trees ready to replace the podocarps are few in numbers, it seems probable that the climax forest is made up of various shade-demanding or shade-tolerating small trees.” In other words, in such places, the physiognomic podocarps have been incapable of self-reproduction for many centuries but to label the developing scrub forest communities a developing climax is to beg the question entirely for, as has been seen, such scrub forest types may, in turn, be replaced by grassland or, seed sources being to hand, they may be invaded and replaced by beech forest of one type or another. Cockayne did not clearly relate the condition of the Banks Peninsula podocarp stands to the most obvious item inviting comparison. The Peninsula was not, at the date of European settlement, entirely forest clad. The dry north-aspect slopes carried tussock grassland through which, to an altitude of 3,000 ft., fallen logs were distributed. In other words the forest had already been replaced by grassland on the drier sites
and regeneration of the podocarps had failed on the moister, facts which, taken together, would appear to lead to the natural conclusion that the causal factor was one and the same in both cases. This could only be a climatic factor and, since failure occurred first on the dry sites, it could only be a decrease in effective precipitation.
The forests of Banks Peninsula were, for the most part, destroyed during the first few decades of settlement. The few stands that survive to this day do so in a strongly modified condition and a clear picture of the virgin forest is now difficult to reconstruct. Totara would appear to have been the most usual dominant with matai and some kahikatea on the lower slopes of the hills. Rimu was of rare occurrence and, over considerable areas, scrub hardwoods formed the bulk of the stands. On the highest ridge crests true totara was replaced by Hall's totara which occurred in association with kaikawaka (Libocedrus bidwillii), an association which will be further discussed below. Certain beech species were represented through on restricted local sites only, reputedly red beech plus black and/or mountain beech. These beech species may well have spread following the gradual elimination of the podocarps but do not appear to have done so to any significant degree. As has been seen, a climatic change adverse to matai may also be adverse to red beech while, as will be seen, black beech is, in the South Island as a whole, typically a relict species. Over and above this, however, the beech species may simply have been prevented from spreading through operation of topographic barriers. Insufficient forest now remains for investigation of these points: the key feature of the Peninsula forests, however, remains that stressed by Cockayne. The dominant podocarps were in active process of extinction and this despite the relatively mild peninsular climate which permits the growth in these remnant forests of many secondary forest species more characteristic of North Island than of South Island forests.
Allan (1926), in his account of the forests of Mt. Peel was very much more optimistic. He described the forest as built up of various groups of associations and sub-associations. On the flood plain of the Rangitata River kahikatea is dominant with smaller matai sub-dominant while totara occurs infrequently. On the terraces, matai is the usual dominant with kahikatea and totara present in lesser amount but totara, in turn, achieves dominance on the drier hill slopes, kahikatea and matai, in that order, losing their place in the stands. Totara persists well up the mountain side but becomes stunted with gain in altitude and is eventually replaced by rata.
Within these stands there are many lesser scrub hardwood forest types (Allan's sub-associations) with one or other of the following species locally dominant, lowland ribbonwood, mahoe, kanuka (Leptospermum ericoides) and the mountain ribbonwood (Gaya ribifolia). Other common associate species, c.f. Waiau Valley forests, include Myrtus obcordata, Melicope simplex, Pennantia corymbosa and Parsonsia heterophylla in its luxuriant form.
Allan makes no mention of the age, form or condition of the forest dominants, a matter of considerable significance as has been seen; and he fails to mention the frequency of occurrence of podocarp advance growth or regeneration for other than the swamp kahikatea of the flood plain. Kahikatea swamp forest is a most unfortunate example to cite as evidence of the vigour of podocarp forest for, as already shown, kahikatea can survive in the swamps throughout
an era of generally unfavourable climate. Even so, misinterpretations are likely. Cockayne (loc. cit. p. 177) described Riccarton Bush, a typical matai/kahikatea swamp stand, as “… still quite vigorous … seedlings kahikatea are produced by thousands.” This was 25 years ago but to-day few if any sapling or pole kahikatea are present. Seedling production is but one phase of forest reproduction. The seedlings must survive and grow.
The various scrub hardwood ‘sub-associations’ present in the Mt. Peel forest were apparently regarded by Allan as normal components of ‘climax’ matai/totara/kahikatea forest whereas all available evidence points to the conclusion that they are purely temporary communities occupying sites where podocarp regeneration has failed. The kanuka community is distinctly impermanent for this species is a strong light demander which cannot reproduce in its own shade. Such communities must be replaced in time by shade tolerant species. The classic view, and the one apparently adopted by Allan, is that all these minor hardwood communities will provide the cover under which the podocarps will again regenerate in a two or multi-phase cycle of forest development. But he described no single instance of the operation of this cycle from Mt. Peel and no instance has yet been described from any other forest of this type in the South Island. If the classic view were correct the forests should be group even aged with a full range of age classes in evidence but not wholly mature, over-mature or senescent as we know them to be.
Mountain beech is present in the forest of Mt. Peel at high altitudes adjacent to the scrublands and alpine grasslands. It is also present in what Allan describes as relict communities on the midslopes and along the streams. He stressed the fact that the mountain beech in these relict communities were all old and unthrifty with little regeneration in evidence though the riparian stands were somewhat younger than those on the midslopes. Allan argued from this that it is the podocarp forest (meaning, presumably, not the podocarps themselves but the associate scrub hardwoods) that is aggressive and that it is the mountain beech which is in course of elimination. But it must be remembered that mountain beech trees are old and overmature when little more than 150 years old whereas the podocarps may be comparatively healthy and vigorous at 800 years. It could not, therefore, be maintained that, because the mountain beech were old and defective, they were therefore in course of elimination. Allan, having regard to Speight's work on the ancient forests of Canterbury, concluded that beech forests and tussock grasslands occupied the Mt. Peel region following the retreat of the Pleistocene glaciers but that later there was a warmer and wetter period during which the podocarp species occupied the area. Mountain beech barely survived on exposed sites. Subsequently there has been a re-development of a modified steppe climate to the east of the main divide but” … podocarp forest persists at Mt. Peel owing to especially favourable rainfall while succumbing elsewhere. Relicts of beech forests are enabled to retain their position but with difficulty and largely succumbing in the Mt. Peel area.” Re-evaluating the evidence, it could be stated that, in the comparatively recent past, matai/totara/kahikatea forest flourished on Mt. Peel while mountain beech survived through chance accidents of site at high altitudes and in quasi-permanent riparian communities, with periodic spread from the streams to rocky knolls and other dry midslope sites. Following recent climatic changes unfavourable to the podocarps, the podocarp stands have stagnated though still displaying some regenerative capacity on deep, moist, lowland
alluvial soils. Hand-in-hand with the gradual elimination of the podocarps on other sites there has been a temporary luxuriant development of the podocarp associate scrub hardwood species or invasion of the stands by the atypical forest species, kanuka and kowhai; but the climate does not yet appear favourable to the spread of mountain beech though general indications are that, had perchance a seed source been present, silver beech would have spread. There is clearly no evidence and no justification for taking the argument back in time to the close of the Pleistocene Ice Age as Allan has done. Many things have happened since then.
Finally, Allan records kaikawaka as a component of high altitude podocarp forest on Mt. Peel where it occurs in association with totara (Hall's totara?) above the altitudinal limits of matai. This was the case in the Banks Peninsula forests also. In both areas Hall's totara/kaikawaka forest types are high altitude variants of the matai/totara/kahikatea complex. Speight, Cockayne and Laing (1911) have given an account of the forests of the upper reaches of the Rakaia Valley (see Locality Map 3), and these forests have been more thoroughly examined during recent years with extension of forest reconnaissances to adjoining valleys. These forests are in very variable condition and have been greatly modified by fire and grazing but local stands remain in near virgin condition. Neglecting the consequences of fire and stock trespass, the forests have totara generally dominant on the lower shady, moist slopes even though these slopes are by far the coldest. Most of the trees are Hall's totara but many are suspected hybrids and a few approach true totara closely. The forest under-stories are dense with heavy growth of broadleaf and other scrub hardwoods. Few of these latter species are those listed as characteristic of lowland matai/totara stands but all the species are common in matai/totara forest at its upper
altitudinal limit. Typical understory dominants are Pseudopanax ferox, Carpodetus serratus, Coprosma linarifolia, Pittosporum tenuifolium, and Suttonia divaricata. All these shrubs, and others, in the Rakaia forests commonly grow to the size of small trees. The usual ground fern is Polystichum vestitum; kowhai locally is present in abundance but cabbage trees are rare.
On the drier and more exposed slopes scrub forest of this same general composition but lacking any living totara is widely developed. On the uppermost forested slopes and towards the valley-head glaciers kaikawaka enters the stands and the understory is enriched with many species of Hebe, Olearia, Senecio, Dracophyllum and other shrub genera typical of the sub-alpine scrublands. The minor podocarps, Podocarpus nivalis, snow totara and Phyllocladus alpinus, mountain toa-toa, also enter the stands. No detailed description can be given here. Much more field investigation must be done. These Hall's totara/kaikawaka forest types are floristically rich in sharp contrast with the adjoining beech forests of these watersheds. Many distinct variations in type can be recognised but the unravelling of the primitive from the induced presents major problems demanding detailed intensive study. Nevertheless it is clear that these Rakaia Valley forest types are closely related to the high altitude forest types of other localities, e.g., Mt. Peel, Banks Peninsula and certain forests in the Dunedin District, where the lowland forests are known to be, or to have been, matai/totara/kahikatea forests.
This relationship was made the more certain by the discovery already mentioned, of a single veteran matai in the beech forest on Mt. Algidus situated some ten miles to the east of the Rakaia totara/kaikawaka stands. Intervening and adjoining tussock grasslands were, in the early years of pastoral occupation, littered with fallen totara logs.
These Rakaia forests have long been assumed to be the only forests of this type present on the eastern flanks of the Southern Alps. Cockayne vaguely related them to floristically similar forests established on the western flanks of the mountains above the Westland rimu/rata/kamahi hill forests. But they are even more widely developed in the Mathias and Wilberforce Valleys, major tributaries of the Rakaia joining the latter near Mt. Algidus; and scrub variants of the same type of forest are developed in the head-water tributaries of the Rangitata River, the valleys of the Havelock, Clyde and Lawrence Rivers. The Clyde Valley is now generally devoid of any forest growth but one remnant pocket of broadleaf scrub forest contains a single living totara while an old photograph of unknown origin shows totara logs being hauled by horse dray down a rocky river bed close up under mountain slopes which, to-day, carry nothing but a mantle of rock rubble and snow. Further odd pockets of related scrub forest types occur around the margins of the MacKenzie Plains and an unconfirmed report is of an isolated stand of Hall's totara/kaikawaka in the Hunter Valley draining to Lake Hawea, where, as already described, matai stumps have been found within the beech forests. In Otago, Hall's totara/kaikawaka stands occur above the matai/totara/kahikatea/rimu forests near Dunedin with the most southerly reported occurrence adjoining remnant matai stands on the hill country to the east of Clinton.
In the Upper Rakaia, mountain beech forest is present near the confluence of the Mathias and Rakaia Rivers. In the Wilberforce, it is widely developed downstream from the Moa Stream. In this area migration patterns in every
way comparable to those developed in Western Southland are traceable and these lead to altitudinal reversals of forest types as mountain beech invades and replaces totara/kaikawaka stands. But these patterns have not yet been studied in detail. Mountain beech is the physiognomic species in the forest on Mt. Algidus and it is the sole tree species present in the third major Rakaia tributary, the Harper.
In the Rangitata headwaters, mountain beech is present near the Havelock tributaries, the Forbes River and Carney Stream, but in this area the forests have been so greatly modified by fire that little could probably be learnt from their study. In general it would appear that mountain beech, in the Rakaia and Rangitata watersheds, survived the podocarp period on more or less randomly distributed sites at high altitudes but usually only on the secondary ranges well to the east of the main divide. It has therefore been unable to invade the disintegrating podocarp stands since the migration paths lie upstream and into the teeth of the prevailing north-west (fohn) winds.
The Rakaia type Hall's totara/kaikawaka stands are, therefore, by no means peculiar aberrant types restricted to the Upper Rakaia. On the contrary, forests of this type must have once occupied the greater portion of the eastern high country with extensive forests developed in the catchments of the Rakaia and Rangitata Rivers and probably also in the catchment of the Waitaki River and rivers to the south. To the north of the Rakaia traces of these old forests hare been lost following the rapid entry of the beech species but, to the south, beech seed sources were either non-existent or were so placed as to render forward movement very slow. And to-day, over wide areas, regional climates would appear to be too severe to permit the development even of mountain beech forests though it is patent that climates once favoured podocarp forests.
A few fragments of the old podocarp forests, of the old matai/totara/kahikatea forests of the lowlands and of the Hall's totara/kaikawaka forests of the uplands, still survive on a haphazard assortment of locally favourable sites but all display unmistakable internal evidence of their existence under essentially hostile regional climates.
The Destruction Of The Forests.
If this contention be correct, namely, that one and the same basic factor underlies both the destruction of the old forests and the present condition of existing forests, then the date of destruction and, by implication, the date of the climate change, cannot be set back very far. Existing matai/totara forests in eastern and inland districts of the South Island are over-mature forests in which the dominant podocarps are, almost without exception, old trees. There are few young podocarps to replace them as they decay and fall. The change of conditions which brought about cessation of effective podocarp regeneration must have taken place during the life span of trees now living and the mean age of these forest veterans is estimated at from 500 to 800 years. Interruption of the regenerative cycle may, however, have taken place on sites now occupied by grassland somewhat earlier than these figures imply, particularly if the climatic change was a progressive one in its initial stages, since existing forests which did regenerate to a final podocarp crop 500 to 800 years ago occupy, on the whole, sites in respect to which local factors would, for a time, counterbalance the growing unfavourable character of the regional environment.
The probable latest date for the change of climate would lie somewhere between the beginning of the 11th and the close of the 14th centuries A.D. On forest evidence it is difficult to set any limit defining the probable earliest date. A late date is favoured by the fresh appearance of the fallen logs even though these were commonly of durable heart totara, frequently charred on the outside. A late date is also favoured by evidence derived through study of the age class distribution of rimu in the hill forests of Westland (vide infra); but, when the magnitude of the changes which have taken place in the rimu/beech forests of Western Southland are considered, an earlier date is indicated. Even in these latter forests, however, the matai of the Dean Hill sandstone ridges, a relatively unfavourable site, became established less than 1,000 years ago.
An alternative line of evidence bearing on this question is that of Maori tradition. Final destruction of the forests, over wide areas, was undoubtedly by fire. But, also without question, the forests were not burnt until after they had entered the period of instability as a consequence of climatic change.
Destruction of stable forests by fire, even if conceivable on such a colossal and universal scale, would inevitably have been followed by slow forest re-establishment but not by pre-emption of the sites by xerophytic tussock grassland. Even with repeated fires some sites would have escaped and some young forests should be present. Many of the localities where fallen logs were found could not possibly be described, to-day, as within the climatic range of podocarp forest. The climatic change occurred either before or after the fires. It could only have been before. Widespread destruction by fire of forests already rendered unstable by increasing desiccation is conceivable.
Maori traditions concerning these fires have been capably summarised by Duff (loc. cit.). His conclusion would appear to be that the traditions date back, at least, to the century immediately following the arrival of the Fleet Maoris, circa 1350 A.D., but, with greater probability, to pre-fleet days. The weight of evidence would indicate that the forests were destroyed by fire before 1450 A.D., probably before 1350 A.D., and possibly as early as 1000 A.D. These Maori traditions relating to the ‘Fires of Tamatea’ refer, of course almost certainly to a series of conflagrations over an extended period of time and possibly to fires in eastern districts of the North Island as well as to fires in the South, not to one single immense blaze sired by the legendary chieftain, Tamatea. There can be little doubt, however, that a substantial basis of fact does underlie the tradition. That considerable fires did rage is indisputable and, although the Maori was capable of fabricating the legend in order to account for the presence of the charred forest remains without actually having witnessed the fires, yet the dates suggested by tradition agree very well with the dates derived through study of remnant forests for the onset of the period of increasing desiccation.
Other evidence is sketchy. If the date for the climatic change be set at about the year 1200 A. D., then this agrees, as pointed out by Raeside, with the agreed dating of the last major climatic change experienced in Western Europe and in the North Atlantic region generally; and most authorities (vide Committee on Glaciers, 1946) appear to agree that temperature changes, rainfall changes being secondary and consequential, occur synchronously in both hemispheres. Lockerbie (1950A), in discussing Raeside's conclusions states, “The evidence present in South Otago settlement sites appears definitely
to support the general conclusions of Raeside. It strongly suggests a larger Polynesia population in South Otago in the 13th century than at any later date.” In other words, it was probably warmer in South Otago then than now and the change of climate and consequently the period of forest destruction were within the experience of the Polynesian inhabitants. On the face of it, also, the reported occurrence of kumara (Ipomoea batatas) pits at Temuka in South Canterbury (Lockerbie, 1950B) where the cultivation of kumera today would be most difficult would also suggest that the warm climatic era lasted well into the period of Polynesian settlement; though kumara may have been cultivated there at some later date during a short period of relatively warm climate.
However, without entering into further detail, it is sufficient for present purposes to state that all evidence to hand strongly suggests that there was a major change in climate and that this change occurred somewhere within the period from the end of the 10th to the beginning of the 14th centuries, most probably about the year 1200 A.D., and that the old matai/totara/kahikatea and Hall's totara/kaikawaka forests were destroyed by fire soon thereafter. Parenthetically, it might be added that, since the destruction of the forests by fire apparently followed closely on the heels of the climatic change, the change itself may have been an abrupt one and was possibly initiated by a period of markedly severe (drought) weather.
But the primary purpose of this report is not allocation of settled dates to the events of Polynesian history nor is it the derivation of fixed dates for the onset of the new climatic era. The purpose is solely the demonstration of the basic instability of existing forests, an instability having its roots in climatic instability; and it is the elucidation of a few of the vast consequential changes in forest composition and species distribution that are in progress. The basic hypothesis adduced in explanation of these various forest phenomena is, nevertheless, seen not to be in conflict with the evidence brought forward by workers in other fields of enquiry. It is, moreover, worth emphasising at this point that the hypothesis of climatic change was originally developed solely through study of the Alton Reversals, without prior knowledge of Raeside's work, without study of the ancient forests, and without acquaintance with the traditions of the Fires of Tamatea. That enquiries pursued separately in such diverse fields lead to the same conclusion might be considered significant.
From this point onwards, however, interpretation of observations made in other South Island forests may be coloured by the desire to lend credence to the working hypothesis. It is not easy, working in the forests, the mountains and the rain, to preserve a completely open mind on these subjects when a few preconceived ideas will serve to reduce the labour involved in critical examination of the forests. The following sections of this report must, therefore, be read in the light of this warning.
Further Notes On The Forests Of The South Island
In these notes no attempt is made at full description of any individual forest of any particular region. The objective is merely to traverse the ground outlining the broad facts of forest type distribution, interpolating a few new facts, and interpreting the whole in terms of the hypothesis of recent climatic
change. Many of the forests have not yet been studied in detail while field work in others is still in progress. Current ideas concerning them are, therefore, in a state of flux but it might, nevertheless, be pointed out that few items have been discovered over the past several years (the first version of this report was written in 1948) that have not proved susceptible of ready explanation in terms of the working hypothesis. No facts have been discovered which would serve in any way to disprove the hypothesis.
The Beech Forests Of Eastern And Inland Districts
It has already been suggested that red beecch forest, during the period of optimum matai forest development, extended well to the south of its present limits. The southernmost stands of red beech of any considerable extent, to-day, are those of Dunton Forest and of the Eyre Mts. to the east of Lake Te Anau. In Dunton Forest, red, silver and mountain beech are all present with, in addition, widely scattered, heavily defective, rimu, miro and matai with a few kahikatea on wet ground. “Red beech is present in small local pockets of limited extent on the moist but freely drained sites of the valley floors and lower slopes but it rarely exceeds 2,000 ft. elevation and is fairly scanty above 1,500 ft. Many of the red beech stands are very much overmature. The trees commonly have broken crowns but there is a fair stocking of saplings and poles where the canopy has been partially opened. Mountain beech × red beech hybrids are fairly common in the vicinity of the red beech sites. Mountain beech is the dominant species over most of the area and is everywhere aggressive except on local sites favourable to red beech and where no drastic opening of the canopy has occurred.” (Williams, 1949). This account could stand, not only for the forests of the Dunton area but also for those of the Eyre Mts. and for those of the Garvie Mts. (Whakaea Forest) which lie still further to the east.
Within each forest the distribution of red beech is essentially discontinuous and it is generally restricted to, and is only vigorous on, sites of exceptionally favourable character. Where it does occur on exposed sites, on dry shallow soils, or on the upper mountain slopes, regeneration is either wanting with invasion of the stands by mountain beech or all advance growth is poor in quality, slow in growth, and is markedly susceptible to insect, fungal or mechanical injury; and this despite the fact that, on such sites, heavy and frequent seed crops are normal. In many stands all the younger stems are of poor form in comparison with the veterans and a stag-headed condition develops at an early stage.
In all these forests red beech appears to be barely holding its ground particularly in Dunton Forest and in the Eyre Mts. forests in respect to which effective precipitation is low. The Whakaea Forest receives much rain from the east as well as from the west and the red beech stands retain a healthier appearance. It might also be noted that, whereas in Dunton Forest there are traces of a former more extensive development of podocarp forest types in the form of relict veteran podocarps, in Whakaea Forest one tributary valley carries, at a high altitude, scrub broadleaf/Hall's totara stands, one ridge crest supports an isolated stand of rata and in one gully bottom there are a bare half-dozen kahikatea. In all these forests hybridism between red and mountain beech is rife.
Vigorous and apparently stable red beech stands are found in certain of the valleys to the north and west of Lake Wakatipu. In these forests there is little sign of any replacement of red beech by either silver or mountain beech, these latter species being typically restricted to the upper slopes, to exposed dry sites, or to local pockets of cold wet ground. In this region effective precipitation is high and the summers are mild and equable though the winters may be very cold with heavy frosts and much snow. No trace has been discovered in these forests of the former presence of podocarp stands though, as usual throughout the beech forests, Hall's totara is present as a minor stand constituent. In the Dart River tributary, the Rockburn, however, a half-acre of kamahi has been found, this species being entirely unrepresented in surrounding forests. Its presence in the Rockburn may be significant. In the Dart Valley, also, groves of cabbage trees and kowhai occur abundantly but, in the absence of other indications of the former presence of matai stands do undue emphasis should be placed on this. Kowhai and cabbage trees are always abundant on old matai soils but they are not necessarily restricted to such soils.
To the north of Lake Wakatipu along the eastern flanks of the Southern Alps, the beech forests display many markedly anomalous features. The distribution of the individual species is discontinuous in the extreme. In the Matukituki Valley which drains to Lake Wanaka, the forests are almost entirely red beech/mountain beech forests though there is one small stand of almost pure silver beech; but in the Makarora Valley which also drains to the Lake, silver beech is the universal dominant and may be the only beech species present, relict stands of matai/totara/kahikatea occupying restricted valley floor sites.
All three species are present in Kidd's Bush which lies on the south-western shore if Lake Hawea but silver beech is present in almost negligible amount and mountain beech is strongly aggressive at the expense of red beech. In the Hunter Valley and in other valleys draining to Lake Hawea, mountain beech is everywhere dominant and may be the only beech species present. This is the case also in all valley forests to the north of Lake Hawea until the Mt. Cook district is reached where, in Governor's Bush, silver beech is the sole beech species. Mountain beech is the only species in most of the beech forests in the Rangitata and Rakaia watersheds but in one small pocket of mountain beech forest on the Arrowsmith Range a single veteran silver beech has been discovered and there are unconfirmed reports that a few red beech are present in the Moa Basin draining to the Wilberforce River.
Mountain beech is again the dominant, and usually the sole species in the forests of the Waimakiriri watershed but small red beech stands occur in its northern tributaries, the Hawdon and the Poulter, and about the confluence of these streams with the Waimakiriri. In these stands red beech again appears to be essentially a relict species in course of replacement by mountain beech and modified altitudinal reversal patterns are in evidence. But the red beech stands in the upper reaches of the Hurunui Valley above Lake Sumner approach those of the Lake Wakatipu region in vigour and local distribution patterns similar to those of the Dart Valley are in evidence. The local climate is also very similar to that of the Dart Valley. The red beech stands of the Canterbury Waiau River (herein called, for clarity, the Waiau-uha River) are less vigorous. Mountain and silver beech are both present as in the Hurunui headwaters and there is local definite replacement of red beech by one or
other of these latter species. These Waiau-uha forests contain clear traces of former matai type stands in the form of pockets of broadleaf scrub forest containing a full range of matai associate scrub species.
The forests of the foothill ranges adjoining the Canterbury Plains, Alford Forest, Oxford Forest, Thirteen-Mile Bush and the forests of Mt. Thomas and Mt. Grey have usually been referred to as being largely black beech (Nothofagus solanderi) forests with more or less mountain beech at higher levels. But these forests are, in actual fact, almost entirely mountain beech forests. Many of the trees on the lower slopes display characteristics intermediate between black beech and mountain beech. Some approach black beech closely, but it is not possible to identify any trees, with certainty, as undoubted black beech. A similar range of intermediate (hybrid ?) forms is found in several other forests lying midway between the plains and the main divide, e.g., in the forest on Mt. Algidus and in the forest in the catchment of Broken River, a Waimakariri tributary.
Most of the foothill forests contain podocarp forest elements. In Alford Forest there are a few kahikatea with one local stand of rata. In Oxford Forest and on Mt. Thomas a few matai, kahikatea and rimu occur in association with mountain beech on the lower mountain slopes and, prior to land clearing operations, were co-dominant with black beech (?) on the adjoining downlands. In these forests, also, there are traces of red beech. In Oxford Forest there is one small stand of red beech a few acres in extent and red beech also occur in association with mountain beech on Mt. Grey.
In south-eastern districts of the South Island silver beech is the only beech species present. Small stands of this species occur within the podocarp forests or surrounded by tussock grasslands on the Horse Range to the north of Palmerston, in several localities near Dunedin, on Mt. Maungatua and at Taieri Mouth. More extensive forests of silver beech are found on the Blue Mts. and in the catchment of the Catlins River.
With respect to all these eastern and inland beech forests it will be most difficult to unravel the full tangled skein of events. The beech forests over very wide areas were destroyed by fire particularly during the latter half of the 19th century as land was sought for sheep grazing; and the fire record probably goes back to the date of the Fires of Tamatea. Many existing forests are wholly young forests, this applying particularly to the mountain beech forests of the drier Canterbury ranges. Nevertheless it is clear that species distributions are not to be explained in terms of the simple static factors of site. The podocarp elements contained within many of these forests are, without question, of relict character as are also those small pocket stands of silver or red beech contained within forests otherwise wholly of mountain beech.
The full story may run somewhat as follows. During the climatic era when matai/totara/kahikatea forests occupied the downlands, foothills, Banks Peninsula and much of the plainland (the more drought subject of the plains soils may never have carried forest), the beech forests survived on random sites in gully and valley bottoms and on certain of the higher hills and mountains. The major areas of beech forest lay to the north of the Waimakiriri River and to the south of Lake Hawea. Between these beech forest regions the matai/kahikatea/totara and the Hall's totara/kaikawaka forests reached back to the main divide.
Survival of pockets of beech forest was at random and so also was survival of the individual beech species but a slight pattern is, nevertheless, traceable. Red beech survived for the most part in the regions centred on Lakes Sumner and Wakatipu with local stands on a variety of sites along the line of the Canterbury foothills and from Hawea south to Foveaux Strait. Black beech occurred in association with matai on the foothills of Canterbury, and mountain beech survived on a random assortment of high altitude sites throughout. Silver beech, alone, survived in the podocarp forest regions of the south-east where the forests were typically of a character intermediate between the matai/totara/kahikatea forests and the coastal climate rimu forests.
With the onset of the period of drier and colder climate the podocarp forests disintegrated and were replaced by broadleaf scrub forest or by tussock grassland, a very rapid development where the forests were burnt. Marginally, the podocarp stands were invaded by beech forest species, a movement in which all of the beech species present may initially have participated; but climatic conditions (save, for red beech, in the Sumner and Wakatipu regions) rapidly became hostile to red beech and to black beech. Stands in which these two species were dominant were then, in turn, invaded by mountain beech. Red beech was gradually eliminated leaving the random relict stands that survive to this day while black beech was submerged in hybrid swarms with the closely related mountain beech. Away from south-eastern districts, conditions at no time became favourable to rapid spread of silver beech which has barely held its ground on those sites on which it survived the podocarp forest period or has been almost entirely displaced by mountain beech. It might also be noted in further explanation of the peculiarities of distribution of silver beech that, in red beech/silver beech/mountain beech forests, silver beech tends to be suppressed. In its site requirements it is completely overlapped by the other two species which are typically faster growing. Under the new climates silver beech extended its range only at the expense of the coastal climate rimu forests and even here, e.g., in the Dunedin district, to an insignificant extent.
Concurrently with these re-adjustments of forests to site, the beech forests themselves, on certain sites, were rendered unstable through increasing desiccation and were replaced, commonly through the agency of fire, by manuka scrublands or tussock grasslands, or survived precariously by virtue of their internal micro-climates. Without question, also, the fires destroyed forests which were, in themselves, fully stable and some of these did not recover since recovery depended entirely on survival of seed sources.
In these ways, in course of 800–1,000 years, a complex mosaic of podocarp forest, beech forest, scrub forest and tussock grasslands was built up. The podocarp stands, at the date of European colonisation of the South Island, were universally relict forests though in varying degree in accordance with varying local climates. The beech forests were sometimes fully stable, sometimes relict, they were sometimes relict as red beech or silver beech forests but, had the species present been mountain beech, would have been fully stable. The tussock grasslands were of equally varied status. Some occupied sites which had been under tussock grassland throughout; some occupied ground which formerly carried podocarp forests which were themselves of varied type; and some occupied soils which had previously supported beech forests. In many cases the tussock grassland occurred within regions still possessed of true forest climates,
areas which should have been under beech forest but in respect to which the time interval in between destruction of the old podocarp forests and European settlement had been insufficient for entry of the beech species; or in respect to which the old, though stable, beech forests had been destroyed by fire without survival of seed sources. And it is entirely probable that even some types of tussock grassland were relict grasslands, i.e., those which had been tussock grassland throughout, the high altitude snow tussock grasslands and the grasslands of the (now) semi-arid intermonts.
This confusion has been worse compounded by the events of the past 100 years, by the fires of the graziers, by the grazing and browsing of sheep, cattle, deer, chamois, wallabies and opossums, and by attempts, sometimes completely successful, sometimes entirely unsuccessful, to replace the indigenous plant communities by communities of exotic species. The essential point to note is that, in dealing with the residual indigenous plant communities, forests or tussock grasslands, we are concerned with an extraordinarily complex set of phenomena, with plant communities of highly varied ecological status. Present difficulties and problems in connection with the management of the forests, of the tussock grasslands, and of the watersheds, stem very largely from this fact.
The Westland Rimu Forests
The forests of the Waiau Valley in Southland are the forests of eastern and inland regions of the South Island in epitome. The forests of the Westland podocarp region are essentially but a large scale development of the Western Southland hill country and coastal terrace rimu forests. In Westland, the beech species are unrepresented from the Taramakau River south to the Paringa River. Between these two rivers the regional topography follows a simple and uncomplicated pattern. Coastal fluvioglacial gravel plains and terraces, broken by deep cut river gorges and river flood plains, rise steadily inland over distances varying from six to twenty miles to the main alpine fault. To the east of this fault the Southern Alps rise abruptly in deeply dissected steep slopes of greywacke and schist to ice-clad peaks. Annual rainfall is everywhere very high, from 100 to 200 or more inches per annum, and the entire region, to an altitude of approximately 3,500 to 4,000 feet was, and still largely is, heavily forested.
Throughout these forests, save on sites of special character, rimu is the physiognomic dominant; but the hill rimu forests are of vastly different character to the rimu forests of the coastal plains and terraces. On the mountain slopes the rimu present are typically old massive trees which stand, widely spaced apart, over a jungle understory in which rata and kamahi are the usual dominants. On the lower slopes there may be from eight to twelve or more of these old rimu to each acre but, with increasing elevation and on cold aspect slopes, these thin out rapidly leaving pure rata/kamahi scrub forest which, in turn, merges into rata/Hall's totara/kaikawaka/scrub-composite forest reaching to the timber line. There are of course, many local variations in this pattern particularly where recent landslides scar the steep mountain slopes or where there are heavy and relatively unstable accumulations of rock debris, but the basic distribution pattern is that sketched out above.
Within these mountainside rimu stands, as was found to be the case in the hill rimu forests in Southland, there are few young rimu. Seedling rimu
are occasionally noted but healthy, vigorous saplings and poles occur with sufficient rarity as to excite comment when seen. By all writers, from Cockayne onwards, the rimu in these stands have been allotted relict status; and the kamahi/rata forest type has been described as a ‘developing climax.’ But there has never been any enquiry relative to the conditions that obtained when the existing rimu were young nor has any serious attempt been made to relate the condition of these stands to the condition of the stands of the coastal plains.
No detailed growth ring studies have been made but judging from the few ring counts carried out and from the size and form of the trees, the mountain rimu typically vary in age from 400 to 800 years, with, on certain sites, all trees in the 600 to 800 year age class. In other words, as in the case of the dominant matai, totara and kahikatea in the eastern podocarp forests, effective regeneration ceased within the period from the 12th to the 14th centuries. A few individual trees became established during later centuries but in totally insufficient numbers for maintenance of the stands. And there has been little survival or growth of seedlings over the past several centuries. As the old trees decayed and fell, the rata and kamahi, already present as subordinate species of the forest understories took the place of the podocarps in the forest canopy. No other explanation of the present condition of the stands is tenable.
The hill podocarp stands of Westland, contemporaneously with both the hill rimu stands of Southland and the matai/totara/kahikatea stands of eastern districts, entered an era of stagnation approximately 800 years ago. One factor, only, could be held responsible, the factor of climate. And though, in the east, there was an undoubted fall in effective regional rainfall, in the west where rainfall totals remain fully sufficient for all forest growth, there must have been a substantial temperature drop.
What, therefore, was the effect of this climatic change on the forests of the lowlands? By and large the rimu dominant stands of the coastal plains are young stands closely akin in type to the stands of the Western Southland coastal gravel terraces. Typically, in sharp contrast to the understocked stands of the mountain forests, they are well to fully stocked; and, in few stands, do the individual trees approach, in diameter, the veteran rimu of the mountains. In the few cases where ring counts have been made, the lowland rimu vary in age from 100 years, or less, to 700 years; but, over substantial areas, the lowland rimu forests are strongly group even aged, a feature that leads to the production of a very characteristic, patchy, mottled texture in aerial photographs of these forests. Older stands, approaching those of the mountains in general appearance and composition, typically occupy all broken ground, gorge and gully walls, inter-terrace slopes, and so on.
A few of the smaller rimu pole or sapling even aged groups have palpably originated through profuse stand regeneration after local wind-throw; but this is usually the case only where the groups are very small. No indication of such an origin can be found for the great majority of the groups. The general impression gained from ground reconnaissance of these forests and from detailed study of the aerial photographs is that of progressive occupation
of the lowlands by rimu spreading out from older stands established on all locally dry sites, i.e., of progressive and somewhat irregular colonisation, by rimu, of lowland bogs and swamps. In other words, the rimu stands of the Westland lowlands appear to share a common history with the rimu stands of the Southland coastal gravel terraces.
Clear evidence, in support of this conclusion, was found in the case of the Southland gravel terrace rimu stands, dead or moribund yellow-silver pine (a species of bog forests) occurring centrally within the youngest rimu pole groups; and the evidence is equally clear in Westland though the bog forest species involved is silver pine (Dacrydium colensoi), not yellow-silver pine.
The Westland coastal gravel plains and terraces are marked by a very extensive development of true bogs, the Westland pakihi. These characteristically occupy all poorly drained ground, e.g., the central portions of the larger terraces and all soils with drainage impeded through heavy iron pan accumulation. On these pakihi, or around their periphery, stands of silver pine (with manuka, various epacrids and other species tolerant of acid bog soils) typically occur; and marginal invasion of the silver pine stands by rimu is usual. “Around these pakihi there is a typical succession from open bog to rimu forest.” In the Okarito area, around the pakihi, there is … “dense manuka which forms a belt several chains wide in many cases. Near the outer edge of this belt scattered silver pine begin to appear and gradually assume dominance. Conditions are still extremely wet. Manuka disappears when silver pine becomes dominant but its place is taken in many cases by mountain toa-toa. This marks the first appearance of rimu which occurs usually as thick young pole stands.” And again, “where thick patches of small pole rimu occur within more mature forest it may be assumed that a pakihi has existed there, and in many cases, investigation will disclose old silver pine logs on the forest floor.”
These quotations from field notes by Forest Survey officers could be extended almost indefinitely. All field officers acquainted with these forests have noted the marginal and progressive invasion of the pakihi by manuka followed by silver pine followed by rimu with other species playing secondary roles. Many striking examples have been cited by Grant (1949) from the Saltwater Forest. In the Lake Brunner region, “… extensive pole stands occur.” In one such stand, “the centre of the stand was open for 10 yards diameter with some tall manuka and 3 fair sized silver pine. Outside this a dense stocking of rimu, 2 inches to 4 inches in diameter, small kaikawaka, small silver pine and small kamahi poles. Gradually the size of the poles increased until at 3–4 chains big trees and poles 6 inches to 8 inches diameter were encountered.” (Morris, J.Y., pers. comm.). Cockayne, (loc. cit., p. 180), realised the possibility of such a succession when he wrote, “… and with the death of the silver pines and the drying of the ground, it (the silver pine forest type) would be replaced by a podocarp association. In this case the isolated silver pine trees or clumps in the general forest mass would be relics of former bog forest.” But Cockayne did not recognise the vast scale on which such successions have operated and still, to a certain extent, operate. In no other way is rimu forest, to-day, extending its range;
and there is a very considerable body of evidence in proof of the fact that this process has been an active one for a long period of time.
Many species, other than silver pine, have undoubtedly played a considerable part in these processes. Kaikawaka, for example, occurs in association with silver pine both in existing silver pine stands and in the young rimu pole stands containing remnant silver pine; and kahikatea, also, may have played some part in the former forest cover of the plains and terraces. To-day in Westland, this latter species is a species of swamp forest. It does not appear to be able to tolerate the acidic conditions found in typical silver pine lands. In the swamps it is the universal dominant occurring in very dense stands but it is widely distributed, also, throughout the rimu stands and, on ‘semi-swamp’ soils, may share dominance with rimu. Furthermore, certain sites of a character intermediate between true bog and true swamp may carry stands, rimu dominant, but containing both silver pine and kahikatea. And if, during some past climatic era, the bog-lands were of greater extent, then, at the same time, the swamp-lands may also have been more widely developed.
Kahikatea, in Westland to-day, is also a characteristic species of the young alluvial soils of recent river flats, occurring on these alluviums in association with matai. Both species, together with totara which enters and locally assumes dominance in the stands wherever soils are stony and freely drained, regenerate freely colonising and forming new stands on fresh river deposits. There is nothing to show that these matai/kahikatea and matai/kahikatea/totara stands are other than a perfectly normal, stable expression of present climate and soil type. But if regional climates have, in fact, been considerably warmer at some recent date, traces of matai should also be discoverable on higher ground on the main mountain slopes and particularly on slopes of warm aspect. No records were available on this point but careful search of one locality on the mountain slopes above the Big Wanganui River ended in the discovery, at an altitude of circa 1,500 ft., of a single veteran matai within a scrub hardwood stand otherwise containing all species typical of relict matai forest.
The Westland forests, therefore, contain all the elements found in the forests of Western Southland though there are, of course, many differences in detail. In Westland, for example, the kahikatea forest types assume a prominence unusual in Southland; and this species, in Westland, displays a vigour unknown in the south. Both kahikatea and rimu attain dimensions, particularly with respect to total height, far surpassing, in the west, anything recorded from the south. Many common Westland forest species, e.g., the liane Freycinetia banksii, the shrubby tree, Quintinia acutifolia, and the shrub Ascarina, lucida, are not found in Southland; and so on. But the essential features of the forests are the same. Each major forest type as found in Westland can be matched against a comparable, or a closely comparable, forest type from the far south. There are no grounds for assuming that such closely related types and type groups differ significantly in origin.
In Westland, as in Southland, indications are that the lowland rimu stands are young stands, that rimu has spread out across the coastal gravel plains and terraces following some change in regional climate, and that the vegetation type so displaced was, over wide areas at least, a type of bog forest such as that now found on many of the Westland pakihi. Simultaneously, the old rimu stands
of the hill and mountain slopes stagnated with assumption of dominance, in the absence of the beech species, by the podocarp associate hardwoods, rata and kamahi. But, in Southland, the rata/kamahi stands are, quite clearly, temporary in character. Their eventual replacement by silver or by mountain beech, granted a continuance of present trends, is certain. In Westland, however, where no beech seed sources are to hand, the rata/kamahi type assumes a measure of relative permanence.
Recapitulating, the lowland forests of Westland are patch-work forests containing rimu stands of all ages and stages of development, containing silver pine bog forest stands likewise of all ages and stages of development, containing kahikatea dominant stands of the swamp soils and the kahikatea/matai/totara stands of the recent alluviums, containing the older rimu stands, the rimu/rata/kamahi stands, of the well drained soils, of the inter/terrace slopes and of the gully and valley walls, containing many residual areas of open pakihi, and containing any or all of these elements in complex and inseparable admixture. Additional to these are those type groups, in part related to the above, characteristic of purely local and specialised sites and soils, e.g., the forest types of coastal dune sands and of the interdune pakihi. But the whole complex is thoroughly comprehensible in terms of hypotheses of recent climatic changes.
One final point, only, might be noted. For the first several centuries of the present climatic era the spread of the forests across the lowlands must have been an extremely rapid process, far more so than is indicated by the rate of spread of silver pine and rimu across the residual pakihi to-day, the probability being that only the most recalcitrant pakihi soils remain unforested. This, if in reality the case, would point to the probability that certain of the open pakihi existing to-day may be stable, resistant to colonisation by forest species; and to the probability that, in other cases, the typical succession, pakihi to forest, will be halted at some intermediate stage, soil conditions prohibiting full development of rimu dominant stands.
Beyond the rimu stage few if any areas of lowland forest have gone. Will there be, under present climates, a second natural crop of rimu on these lowland sites? Or are the rimu dominant stands as temporary in character as were the silver pine stands they replaced? These questions cannot yet be answered with confidence though it is generally obvious that, the older the rimu stands, the stronger the representation, within them, of the scrub hardwoods. Current indications are, therefore, that, on many sites at least, the rimu stands function as nurse crops to scrub hardwood stands, a challenge to the ingenuity and skill of foresters.
The South Westland Beech Podocarp Forests.
With one exception, vide infra, the beech species are not represented in the forests from the Taramakau to the Paringa River. This situation has been discussed at some length by several authors, the latest treatment of the topic being that of Willett (1950). There is general agreement that the underlying cause must lie as far back in time as the last major advance of the Pleistocene ice for the region from which the beech species are absent is roughly co-terminous with the area occupied in its entirety by great piedmont glaciers. Re-occupation of the ground on the retreat of the ice by the podocarps and by their associate hardwoods could be fairly rapid since all of these species possess either very
small seeds susceptible of wind carriage over great distances or their seeds are subject to carriage by birds. But the beech species, neglecting the possibility of water carriage of seed, move very slowly.
Invasion of the Westland podocarp region by the beech species could only be from the north or from the south. To the east all potential seed sources are sealed off by the ice barrier of the central portion of the Southern Alps. There are but the two ice-free passes over this section of the main divide and, in both of these cases, the forests to the east of the divide are Hall's totara/kaikawaka forests, not beech forests.
But, to the south of the Paringa River, beech forests are widely developed and it seems probable that beech forest nuclei have here survived not only the full period of the last major advance of the alpine glaciers but also subsequent period (s) of warm podocarp favourable climate. And these beech forests are now linked, by way of several passes long ice free, with the beech forests to the east of the main divide.
No descriptions of the South Westland beech and beech/podocarp forests have ever been published; nor is a complete account within the scope of this report. Briefly, the coastal lowlands about and to the north of the Haast River and from the Haast south to the Waiatoto and Arawata Rivers carry podocarp stands generally similar in type to those of the main Westland coastal plains though, in the south, the pakihi are of wider extent, the forest types of the coastal sand dune complex are more prominent, and the lowland podocarp stands contain a strong, local, beech forest element, both silver beech and mountain beech being represented on a wide variety of sites. The southern hill forests, on the other hand, are predominantly beech forests with a very variable podocarp forest element.
In the hill forests to the north of the Haast River, silver beech is the main, and is commonly the sole, beech species present. Silver beech, in varying admixtures with rimu, rata and kamahi, is a common dominant in the forests of the broken hill country immediately to the south of Lake Paringa, though, particularly coastwise, these hill stands may contain no beech and are then identical with the rimu/rata/kamahi hill stands to the north. But inland on the slopes of the main ranges, extensive pure stands of silver beech are developed. In general it would appear that there has been a fluctuating advance of the beech species northwards into the Westland podocarp region, a slow advance largely without benefit of water carriage of seed and, in respect to the lowlands, through relatively stable podocarp forest types. The beech ‘front,’ to-day, lies along the line of the Paringa River though there are random silver beech outliers northwards to the Mahitahi River. These, possibly, are relict from some period during which the beech ‘front’ lay further to the north than it does to-day, though this could not be claimed with any certainty; but that the advance northwards of the beech species has been a fluctuating advance is evident from the fact that the northernmost stand of mountain beech (on Bald Hill, a few miles to the south of the Paringa River) is clearly a relict stand. Mountain beech here occupies a broad hill crest and appears to have survived a period of hostile climate as a species of a bog forest.
To the south of the Haast River the forests of the foothills abutting on the coastal lowlands are of most varied character. One interfluve may carry pure stands of silver beech; the next, kamahi/rata/rimu, kamahi/rata or Hall's totara/
kaikawaka/scrub-composite stands devoid of any silver beech; and the next interfluve may carry mixed beech/podocarp stands passing upwards into either pure silver beech stands or into Hall's totara/kaikawaka stands. The type of forest developed on any one spur or interfluve appears to be wholly without relation to local factors of site and to be entirely the result of historical accident. Altitudinal reversal patterns are locally in evidence though seldom strongly pronounced, one usual feature being the restriction of mountain beech to the lowlands with silver beech, alone, on the hills.
Red beech enters into the composition of the stands in the Arawata Valley. In the lower reaches of the valley the forests are largely silver beech forests with a variable development of rimu/rata/kamahi and related forest types, these being found particularly on sites and slopes of cold aspect. Red beech, in this sector of the Arawata Valley, plays an insignificant part, a few isolated trees or groups of trees occurring on riparian sites; but, upstream toward the confluence of the Arawata and Waipara Rivers, red beech rapidly increases in abundance. The riparian stands became continuous, widening and expanding out across the lower slopes of the mountains until, toward the valley head and close to the main ice fields of the Olivine and Dart Barrier Ranges, red beech is the universal dominant to a point a few hundred feet short of the timber line, silver beech stands being found at the timber line.
This is a reversal pattern on a grand scale, the more mesophytic species, red beech, being the dominant species in the forests close to the main ice-fields and the cold climate species silver beech, the dominant species on the warmer hill sites close to the coast. Mountain beech, in the Arawata Valley, has only been found, to date, confined to remnant bog forest stands along the valley floor, occurring in close association with silver pine and kaikawaka. On the valley floor, also, small stands of swamp kahikatea are found and a few sites intermediate in character between bog and swamp carry very variable stands which locally contain all three beech species together with kahikatea, kaikawaka, silver pine, rimu and miro plus the scrub hardwood species, rata, kamahi and pokaka.
These complex Arawata Valley forests have not yet been studied in detail but, from the foregoing account, it will be evident that they are unusual in structure with red beech, in particular, behaving in unorthodox fashion. In these forests red beech displays no great vigour and the probable explanation is that it is here a near relict species. Silver beech, following the climate change, has been able to extend its range invading and replacing the old hill podocarp/rata/kamahi stands but the red beech stands have remained in a static condition barely holding the ground occupied during the podocarp climatic era. And examination of the distribution of red beech in the forests to the south of the Arawata lends strength to this view.
To the south and west of the Arawata Valley, the forests are largely mountain beech/silver beech forests with local representation in the beech stands of rimu, rata and kamahi and, on valley floor alluviums, local development of kahikatea or of kahikatea/beech/rimu stands, morainic hollows and other boggy ground commonly supporting scrub stands of mountain beech, silver beech, silver pine, yellow-silver pine and manuka. But, within these forests, a few trees of red beech have been found on the hills lying between the Jackson and Martyr Rivers and about the confluence of the Martyr and Cascade Rivers. A red beech stand, a few acres in extent, lies to the south of the Cascade River on valley floor alluviums
close to the Hope River but no further red beech occur until, some twenty miles to the south, red beech/rimu stands several hundred acres in extent are found on warm aspect slopes immediately to the south of Big Bay and within a mile of the coast.
Red beech stands are also found throughout the valley forests of the Pyke and Hollyford Rivers but, once again, distribution is strictly discontinuous. Some stands occupy deep silt soils along the valley floors but others occur on the steep mountain slopes at almost any altitude up to the timber line, indiscriminately on slopes of warm and cold aspect; and these stands vary in size from a few hundred acres, more or less, to minute stands containing but a dozen or so trees.
The only possible explanation of this gross discontinuity is that, in this region, red beech is a relict species surviving, by chance, on a random and miscellaneous assortment of sites. Silver beech, to-day, is universally the aggressive species in these forests, mountain beech achieving dominance only on sour bog-forest soils and on very shallow soils subject to periodic drought, e.g., on glacially rounded spurs and roches moutonnees. And the podocarps, equally with red beech, are relict on South Westland hill sites wherever they occur, the podocarp stands retaining some slight regenerative capacity only on the warmest of the valley floor alluvial soils. On hill sites, seedling, sapling or pole podocarps are encountered but rarely.
To consider one further item: matai, in these forests, is occasionally found on the valley floor alluviums but occurs in quantity in one stand only. An extensive stand of matai, in association with kahikatea and rimu, occupies the bay infill alluviums at Big Bay. This stand is senescent in the extreme. The physiognomic podocarps, one or two per acre, are massive, ancient trees which tower over a low underwood of scrub hardwood species, fuchsia dominant. Save for a few kahikatea, no podocarps conceivably less than five or six hundred years of age ire present; and silver beech invades the stand peripherally and along all water-courses running through it. In this case, therefore, even the matai of the young alluvial soils cannot be other than relict.
Forest type distribution patterns in these South Westland forests are not straightforward. The region is one of complex topography with soils derived from a wide range of rock types, gneissic rocks, schists, tertiary sediments, recent alluviums, etc., and there are extensive barren lands where ultrabasic peridotites outcrop or where mature podsols have formed on plateaux carved from Pliocene gravels. And any full account of the forests of the region would have to detail all the multifarious variations in forest composition and condition consequent on this wide range of sites and soils. Nevertheless, it seems clear that no successful account of the forests could be given without reference to the hypothesis of climatic change. These forests are not normal in structure but the abnormalities in evidence are entirely explicable on the assumption of recent climatic instability.
Finally, reference must be made to the one exception to the rule of no beech species in the podocarp forests from the Paringa (or, more accurately, from the Mahitahi) northwards to the Taramakau. Beech stands (mountain beech or silver beech, identification is uncertain) do occur in the gorges of the Karangarua River. The only extant account of these stands is that of Harper (1895). They have apparently never been inspected by a botanist or forester and their existence has been at all times disregarded in discussions concerning the Westland podocarp region.
The most likely explanation is that the species concerned has reached the Karangarua Gorge from the upper valleys of the Mahitahi and Makawhio Rivers in which ease these vallevs should contain some stands of beech to-day. It should also be possible to demonstrate the route of species migration from these valleys into the Karangarua and the Karangarua stands should lie down-river from the point of seed entry into the valley. Other potential seed sources lie to the east of the Karangarua in the Landsborough Valley but these are unlikely to be the true sources since they are sealed off by the ice barrier of the Hooker Range.
It is on test cases of this sort, and on their satisfactory solution, the confidence in the validity of the hypothesis propounded in this report has been built up. In the present case, if the above explanation of the origin of the Karangarua stands should prove to be correct, then belief in the accuracy of this account of the Westland forests will be strengthened. But if the explanation should prove untenable, if, for example, the Karangarua stands should prove to be relict stands dating back through both the podocarp climatic era and the period of the last major glacial advance, then this account is wrong, wholly or in part, or has been grossly over-simplified, this latter being the most probable fault.
The Beech/Podocarp Forests Of North Westland And Western Nelson
In North Westland the beech forest ‘front’ lies, to-day, generally along the line of the Arnold and Grey Rivers though there are significant outliers south to the Taramakau. To the north of the Ahaura River and the Grey, the forests are largely beech forests containing a strong podocarp forest element but with pure stands of podocarp species restricted to local and specialised sites. To the south of the Ahaura, the forests are mainly podocarp forests of the Westland type though with a strong, in-coming, beech forest element.
In comparison with the Western Southland story, however, the North Westland forest story is a complicated one, the complicating factors being several.
In the first place, in Southland, but two species of beech were involved in the forward movement of the beech forests into the podocarp forest region, silver beech and mountain beech; but in North Westland four species are involved, red beech, hard beech (Nothofagus truncata), silver beech and mountain beech. Secondly, whereas, in Southland, migrations patterns are simple reflecting a straightforward downward movement of the beech species into the coastal podocarp stands, in North Westland, not only did beech forest nuclei outlast the podocarp forest period on high altitude sites on the mountains but several of the beech species also survived on certain lowland sites, e.g., mountain and silver beech as species of lowland bog forests. Thirdly, in Southland, the movement of the beech species was, essentially, a unidirectional movement from the mountains southward to the coast, but in the north-west, in so far as the forests of the Grey and Inangahua Valleys are concerned, the movement has been multidirectional, eastwards from seed sources on the Paparoa Range, westwards from seed sources on the main divide and on the Victoria and Brunner Ranges, southwards down the Grey River, northwards down the Inangahua River and outwards from surviving lowland seed sources. Fourthly, in North Westland, the patterns of change tend to be blurred for, in this region, site requirements for red beech and hard beech on the one hand, and for rimu on the other, overlap to a considerably greater extent than was ever the case for silver beech, mountain beech and
rimu in Southland. In other words, rimu maintains a place within developing red or hard beech stands with greater facility than it does in silver or mountain beech stands, replacement of rimu by red beech or hard beech seldom, therefore, proceeding to completion. And finally, as may have been the case in Southland forests to the west of the Waitutu River, there is, in North Westland and in Western Nelson, frequent super-imposition of two distinct processes, the one, invasion of various types of bog forest by rimu and the other, invasion of the rimu stands by one or other of the beech species.
These forests have not yet been studied in as great a detail as have been the simpler Southland forests so that it is not yet possible to present a full account of them. All that can be attempted is the selection and brief description of a few significant items.
In the forests lying to the south of the Ahaura River, to the east of the Grey River, and to the north of the Taramakau, migration patterns similar to those described for Southland forests are traceable though they have been somewhat obscured by the effects of a full century of gold-mining and timber logging. Primary seed sources for silver beech and for red beech appear to have been high altitude stands toward the headwaters of the Grey and Ahaura Rivers. For mountain beech the primary seed source would appear to have been the bog forests of the lowland pakihi. For all three species additional seed sources on the Paparoa Range and in the hill country to the south of Reefton were tapped by western and northern tributaries of the Grey River. Entry of species into the region would, therefore, have been rapid but their subsequent spread to the south has been extremely slow for, latterly, migration routes have no longer paralleled stream and river courses. Broadly speaking, there has been a slow infiltration of the beech species through the lowland podocarp stands, a movement across interfluves accompanied by periodic rapid fingering out of the beech stands down secondary streams, a pattern somewhat distorted by the residual pakihi around which (or from which, since, in certain cases, they were in themselves beech seed sources) mountain and silver beech have spread more rapidly. By the time the line of the Arnold River is reached, the beech species are present on riparian sites only and all interfluves are still occupied by Westland type podocarp stands. To the south of the Arnold the forests are typical Westland podocarp forests and contain little beech of any description save for a few small pockets, principally or entirely of red beech, occupying sites suggestive of stand origin from seed sources along the lower reaches of the Grey River.
Red beech is again present in the Taramakau Valley with the main stands upstream from the confluence of the Taramakau and Otira Rivers. These stands appear to be of entirely different provenance to those of the Grey and Arnold Valleys from which they are separated by a broad belt of uninterrupted podocarp forest. The only traceable connection they have with other stands of red beech is by way of the Taramakau River itself. In other words it is suggested that the primary seed source for the Taramakau red beech is to be sought in the beech forests to the east of the main divide, the Hurunui Valley and Lake Sumner red beech stands. That red beech is but a recent entrant into the Taramakau is strongly suggested by the forest type distribution patterns in evidence about the Otira-Taramakau confluence, typical altitudinal reversal patterns of the Southland type with podocarp and podocarp associate scrub hardwood forest types lying above the red beech stands.
In the Ahaura-Taramakau forests we have, therefore, all the standard Westland forest types, the relict rimu/rata/kamahi stands of the hill slopes, the lowland rimu stands of varying age, the kahikatea swamps and the kahikatea/rimu stands of partially swampy soils, the kahikatea/matai stands of the recent alluviums, the silver pine pakihi, and all the many intergrading types of forest. And, superimposed on this basic pattern, are the migration patterns of the incoming beech species with additional new types of forest produced through long continued survival of mountain and silver beech in association with silver pine and kaikawaka around the pakihi.
One final point remains for mention: the precise part, if any, played by hard beech in this forward movement of the beech forests into the Westland podocarp forest region, is not known. Hard beech is present in abundance in the forests to the north of the Ahaura but its distribution in the forests to the south has not yet been studied.
To the north of the Ahaura River, as already mentioned, the various beech species are generally dominant. In the Grey and Inangahua Valleys the forests of the valley floor alluviums are variable in type but are mainly kahikatea/silver beech/red beech/rimu stands containing, locally, a few matai, and any one species, save matai, may be dominant. Red beech, however, is universally dominant, typically in association with scattered rimu and small kamahi, on the lower valley slopes. These red beech stands pass upwards into hard beech stands which occupy the steeper and drier slopes and ridge crests, rimu again being present though the understory species changes to Quintinia. A few rata occur on these hard beech ridges and there is local development of rimu/rata/kamahi stands.
The hard beech stands, in turn, wherever the valley slopes continue upwards unbroken, pass once more into red beech stands but these upper slope red beech stands contain few rimu. They persist upslope, with increase in abundance of rata, to 2,000–2,500 ft. at which point silver beech again appears, assuming dominance close to the timber line. Silver beech is the common timber line species throughout the region.
This is the basic species distribution pattern for these forests as a whole. It is a simple pattern and in it there are few indications of any radical changes in progress. The local ridge crest rimu/rata/kamahi stands are suggestive of such changes as is also the general disproportion in the numbers of old and young rimu in the stands; but generally the forest types within the pattern appear fully stable with species distribution governed by temperature factors (coupled with altitude) and soil moisture factors (coupled with angle of slope and exposure).
This basic pattern is, however, seldom developed in such a simple form. The foothills lying between the main rivers and the mountains are carved from immense thicknesses of gravels. And on these gravels, wherever level or near level ground occurs, a pakihi or pakihi type bog forests are found. In other words, a complex topographically controlled pattern of bog forest types is, over the greater part of the region, super-imposed on the basic regional pattern; and it is in these bog forest types that the greater interest for present purposes lies.
On the Westland coastal gravel plains, as already described, the open pakihi are marginally invaded by manuka, silver pine and rimu, in that order. This gives rise to a series of forest types portraying all the various stages in the development
of rimu stands. In Southland, on the gravel terrace lands to the west of the Waitutu River, these processes of pakihi colonisation by rimu were rendered more complex by the presence, around the pakihi, of silver and mountain beech or by their incoming at an early stage. Similar complications are usual in the forests to the north of the Ahaura River. Rarely, in these forests, simple colonisation of the pakihi by manuka, silver pine and rimu is encountered but this is usually followed by invasion of the developing rimu stands by red beech or by hard beech or by both, giving rise to a series of forest types marked, in a sub-mature stage, by stands of rimu over an understory of younger red beech or hard beech, the stands frequently containing relict silver pine, kaikawaka or even large old manuka. In the majority of cases, however, mountain and/or silver beech are also present from the start in which case these species advance with the manuka, or but a short distance behind it, across the pakihi. On such sites both species remain stunted with production of dense thickets through which silver pine aid kaikawaka appear. Rimu then marginally invade the stands finally giving rise to rimu stands over a relict underwood of mountain beech, silver beech, silver pine and kaikawaka. And at a later stage these stands in turn, may be marginally invaded by red beech or by hard beech.
In other cases, notably at higher altitudes, rimu, red beech and hard beech may play no part in the sequence of events and the final stage in forest development is then marked by little more than the development of stunted stands of silver beech or of mountain beech with, at these altitudes, some bog pine or yellow-silver pine. The possible permutations and combinations are almost endless and no two bog forest stands, in this region, are quite the same in specific composition. Even rata and kamahi may, in certain cases, enter the stands, usually at a fairly late stage in stand development.
To cite one specific example: on a broad flat-topped gravel terrace above the Snowy River a few miles to the north of the Grey River, there is a stand characterised by the presence of widely spaced rimu, the trees being of considerable girth with big canopies though they are of short total height. These short rimu over-top a stunted underwood of mountain beech and silver beech through which are scattered kaikawaka, silver pine, stunted rata and kamahi, and dead stems of manuka. And, peripherally, the stand also contains some red beech and hard beech.
The origin of this stand is thought to have been, firstly, the establishment, by bird carriage of seed, of rimu within manuka thickets dotted over a pakihi bordered by a fringing stand of mountain beech, silver beech, silver pine and kaikawaka. The rimu soon over-topped the manuka thickets with consequent development of spreading canopies and short massive boles. Secondly, the fringing stands closed in over the pakihi with later incoming of rata and kamahi and active suppression of manuka; and, thirdly, with continued lowering of water-tables, red beech and hard beech have marginally invaded the stand, spreading upwards from the terrace slopes below.
Confirmation of this hypothetical scheme of stand development was later obtained by the finding, in another area not many miles away, of an earlier stage in stand development. In this case the greater part of the gravel ridge crest was still occupied by open pakihi but, on local raised mounds, there were manuka thickets containing heavily branched rimu saplings. And around the pakihi
there were fringing stands, in active course of advance over the open ground, composed of silver beech, mountain beech, silver pine and kaikawaka.
In these two stands we have an adequate explanation of the age structure of certain of the lowland rimu stands of the Westland coastal plains. In one such stand the age of the rimu dominants varied from 150 to 700 years but with the bulk of the crop in the 300–400 year age class. The older trees might well be of comparable origin to the rimu of the Snowy River stand, scattered trees established across the old pakihi on local raised mounds or on pockets of otherwise dry ground. By the time these were 300 years of age, occupation of the remainder of the open pakihi by rimu proceeded fairly rapidly, the last few gaps being filled 150 years ago. Unfortunately no note was taken, at the time, of the form of the older trees in comparison with that of the younger.
But to return to the Snowy River stand: why did it not develop over its entire extent as a rimu pole stand? This stand lies close to the altitudinal point at which, in the basic regional forest type distribution pattern, the midslope hard beech/rimu stands give place to the red beech/rata stands of the upper slopes, i.e., at about the altitudinal limit for rimu. Rimu is a shade tolerant species but not on marginal sites. Where climatic conditions border on the unfavourable, rimu requires almost full light for adequate growth. This it obtained, in the present case, in the open manuka thickets but rimu seedlings and saplings do not long survive under the dense canopy of bog forest silver or mountain beech. Once these two species had closed in over the old Snowy River pakihi, the stand could no longer develop as a rimu stand.
Unfortunately, opportunities for study of undisturbed pakihi are rare. All but the most inaccessible pakihi have been burnt and re-burnt in the course of their exploitation for silver pine produce, even long fallen logs being eagerly sought for the durable post timbers they contain. The above account of the processes of pakihi colonisation has been built up mainly through analyses of older stands and reconstruction of their probable modes of origin, deductions supported, in a few instances, by examination of virgin pakihi. But, by and large, the open pakihi typical of Westland to-day have been so strongly modified by fire that we no longer deal with natural but with induced plant communities. It might also be noted that, in at least one instance, the Mai-Mai pakihi of the Grey Valley, a fire history dating back to pre-European days is thought probable, forest types bordering this pakihi bear traces of very ancient fires. This burning of the pakihi by the Maori is by no means improbable for the pakihi were the only open spaces within heavily forested regions and pakihi vegetation, during even short spells of fine weather, is highly inflammable; and the Maori used fire.
Degradation processes with forested lands reverting to pakihi also occur though on a purely local and minor scale. In almost every case so far examined, the initiating factor has been a local change in direction or freedom of stream flow. On the other hand, and on a major or regional scale, degradation of forest to pakihi has occurred in the past, possibly many times, for most of the larger pakihi contain buried timbers; but the process of to-day is the colonisation process and this process of pakihi invasion by forest has been in full operation on a regional scale for many centuries.
Before abandoning the topic of the pakihi, it must be emphasised that not all forest types extraneous to the basic regional forest type distribution pattern
are of pakihi origin. Some stands, though very closely resembling the forest types developed on old pakihi lands, owe their condition to other factors, e.g., to the shallowness of forest soils on glacially over-ridden granite spurs or to the general infertility of certain sandstone soils which, particularly when subjected to excessive ground water seepage, typically carry stunted stands of silver beech or mountain beech with many common bog forest species. In fact, in respect to extensive areas of forest in North Westland and in Western Nelson, lithological factors of site assume very great importance in the control of forest type distribution and may distort the basic regional distribution pattern almost out of recognition.
If the forests of the Paparoa Range to the west of the Grey and Inangahua. Valleys were here to be described, it could only be in emphasis of this point. Limestones, sandstones, siltstones, shales, conglomerates, breccias, coals, greywackes, granites and gravel beds may all outcrop within an area of radius but a mile or two. With additional type variations due to variations, frequently gross, in aspect and in altitude the forests become a veritable jig-saw puzzle of miscellaneous forest types. And for such forests, if they are to be understood, it will first be necessary to establish the validity, or otherwise, of the hypotheses advanced herein, later applying the knowledge so gained toward disentanglement of the more complex.
Studies of the Paparoa forests are in progress as are also studies of the forests of the lithologically complex, topographically rugged mountains to the north of the Buller River. The forests are mainly beech forests with local development of podocarp stands on lowland sites, with beech podocarp stands on the lower hills, and with extensive development of bog forest types at a variety of altitudes. Hard beech plays an increasing part from the northern Paparoas, where extensive hard beech/rimu stands are developed, northwards to the West Haven Inlet; and, from south to north, there is a steady incoming of forest species more typical of North Island forests. Thus, in the far northwest, such species as northern rata (Metrosideros robusta) and pukatea (Laurelia novae-zelandiae) enter the lowland stands, together with many northern shrub species. In the far north-west, also, even matai regenerate freely on deep lowland alluvial soils, e.g., in the Aorere Valley; and the matai seedlings and saplings display fair growth. But this is simply to say that site conditions, in these northern valleys, now aproximate those conditions which must have once been normal for hill sites in the far south.
For the moment, but one further matter in connection with the forests of North Westland and Western Nelson remains for discussion. It has already been remarked that silver beech is the typical regional timber line species. Mountain beech is universally represented in the forests of the lowlands and, as a species of bog forest types or as a species of stands developed on infertile sandstone soils, it may closely approach the timber line; but, save in rare cases, it does not occur at the timber line. On the other hand, in one or two instances, red beech is the timber line species, despite Cockayne's emphatic disbelief in such a possibility (Cockayne, 1926, p. 34).
On Mt. Harata near the confluence of the Grey and Clarke Rivers, red beech, silver beech, hard beech and mountain beech are all present in the forest on the lower slopes. The mid-slopes carry red beech/hard beech stands, the upper slopes red beech, only, with rata achieving co-dominance toward the
timber line. On Mt. Elliot, a few miles to the south of Mt. Harata, red beech/rimu stands occupy the lower slopes, red beech the mid and upper slopes with a few scattered rata and silver beech appearing toward the timber line. At the timber line a few kaikawaka and Hall's totara with scrub composite species are present. And both on Mt. Harata and on Mt. Elliot, wherever red beech is the timber line species, the timber line itself lies 1,000ft. or more below its normal altitude, i.e., below the regional timber line.
These are abnormalities not readily explicable. The few silver beech present in the timber line stands on Mt. Elliot do not appear vigorous and display scant tendency to spread though site conditions would appear thoroughly normal for silver beech. There may be some relation between conditions of Mts. Harata and Elliot and conditions obtaining in certain places on the Brunner and Victoria ranges where the timber line silver beech stands are marked by the presence of many standing dead trees, the living stand being largely composed of smaller, stunted, shrub form silver beech; or there may be some link with present conditions in certain areas on the Paparoa Range where the timber line silver beech stands are opening up with incoming of sub-alpine herb-moor and grassland species. But if, in fact, a regional lowering of the timber line is in progress, the normal expectation would be for a parallel lowering of all forest types but not the complete destruction of the timber line type leaving the species of the mid-slopes to hold their place.
Elucidation of these puzzles of the timber lines might well throw a clearer light on the many outstanding problems of the valley forests.
The Beech Forests Of Inland Nelson
From Foveaux Strait in the south to the Lewis Pass in the north, the main mountain axis of the South Island lies consistently close of the western coast, dividing the island sharply into the wet western and the drier eastern and inland regions. But to the north of the Lewis Pass, the main divide swings away to the north-east with consequent interpolation, between the wet heavily forested mountains of the west and the dry eastern ranges and plains, of a wide mountainous region of intermediate rainfall. This inland mountain region is one of extensive beech forests, the forest mass being broken only by narrow threads of farmland along the rivers, by bracken covered hills adjoining the farmlands where the forest has been cleared in unwise attempts to farm beyond the limits of alluvial soil, and by open mountain summits above the timber line.
Detailed studies of these forests, on a regional scale, have not yet been made but, wherever the forests have been inspected, they have been of remarkably uniform composition though the stands have been by no means in uniform condition. The podocarp species are sparsely represented but red beech, silver beech, hard beech and mountain beech are all present and there are also traces of black beech. The forests of two areas, only, will be described, the forests of the Upper Maruia Valley and the forest known as Big Bush which lies immediately to the north of Lakes Rotoroa and Rotoiti. These two forests are, very nearly, the wettest and the driest of the Central Nelson forests and, broadly speaking, all other regional forests are of intermediate character.
In the Upper Maruia Valley, i.e., upstream from the Maruia River–Warwick River confluence, red beech is the dominant species and these red beech stands surpass even those of the Lakes Wakatipu and Sumner regions in quality.
Growth rates are high, tree form is exceptionally good, and the stands regenerate rapidly and prolifically following any major disturbance of the forest canopy.
Silver beech is present throughout the red beech stands as a sub-dominant species and achieves complete dominance in the uppermost belt of forest, from 3,700–4,000 ft., toward the timber line. At these altitudes it is commonly the sole canopy species present. Mountain beech on the other hand, is commonly found on riparian sites only, and may be altogether absent over wide stretches of forest. Mountain beech is a common dominant in the forests of the Lewis Valley with which the Maruia forests are interconnected across Lewis Pass; and a few mountain beech are established in the Maruia red beech stands immediately below the Pass but these show little sign of active spread. Similarly, mountain beech stands are found on Rahu Saddle which lies between the Maruia and the Inangahua Rivers but these stands, also, appear static.
Hard beech, present in the Inangahua Valley and in the Maruia Valley down-river from the Warwick confluence, is a minor species, if represented at all, in the Upper Maruia stands. Rimu, also, occurs rarely if at all. But a few matai and kahikatea are present on alluvial soils on the main valley floor and there are minor areas of scrub hardwood forest containing typical matai associate species. Kamahi and rata, where present, are small shrubby trees which do not enter the main forest canopy.
There are thus few indications that the red beech stands of the upper Maruia Valley are other than fully stable, perfectly in balance with present climatic and other environmental factors as they obtain in this valley. But, as already described, the timber line silver beech stands on the Victoria and Brunner Ranges to the west are in an abnormal condition with standing dead stems over-topping the present living canopy even though the latter does appear to have reached the culminating point in height growth. And similar conditions are apparent in other timber line silver beech stands on the ranges about the headwaters of the Maruia River. It would seem probable, therefore, that there has been some recent change in climatic conditions at the timber line and. therefore, also in the valley.
This change possibly underlies, in part, the apparent susceptibility of certain of the Maruia red beech stands to damaging attack by bark beetles, the red beech dominants over extensive areas having been killed within recent years by the beetle Nasciodes enysii. And where the red beech dominants have been killed there is a marked tendency for the previously sub-dominant silver beech to assume complete dominance. In other words, is the beetle but the agent of change, the real cause lying in an effective temperature drop? It is, perhaps, suggestive that the centres of bark beetle infestation are those red beech stands occupying sites on or near the valley floor and therefore probably subjected to the heaviest winter frosts.
One final point: the regional timber line lies at about 4,000 ft. above sea level; but, as already noted, on Mts. Harata and Elliot (not far distant from the Maruia Valley as the crow flies) the timber line falls to less than 3,000 ft.; and, on the Brunner and Victoria ranges to the west of the Maruia, it locally rises to approximately 4,500 ft. There is a range, therefore, over a matter of twenty miles or so, of 1,700 ft., approximately 2,800 ft. to 4,500 ft., a feature not to be accounted for in terms of varying rainfall or temperature. One thing
is certain, timber line phenomena are more complex than was visualised in the only study made, to date, of New Zealand timber lines (Zotov, 1938).
In the Maruia Valley, the few observable changes in progress are probably the outcome, solely, of a temperature drop. Rainfall totals remain sufficient for all of the species concerned. In Big Bush, however, both temperature and rainfall factors are clearly involved and there is substantial evidence pointing to major, recent, and continuing changes in species and forest type distribution. Big Bush has been covered in detail by ground and air survey so that the following account, paraphrased from pertinent sections of an unpublished survey report by W. J. Wendelken, is reasonably complete.
The forest of to-day is but a remnant of a once far more extensive forest which once stretched unbroken almost to Tasman Bay. On the coastal plains and in the lowland valleys the primitive forests were podocarp forests with matai, totara, kahikatea and rimu the principal species, some black beech being present in the stands throughout. On the foothills, rimu with red beech and silver beech were the main species, these three species also occupying valley floor sites inland though some kahikatea, matai and black beech persisted inland to the limits of the present forest. In Big Bush, to-day, red beech, silver beech, hard beech and mountain beech are all represented and, on certain sites, some of the mountain beech are scarcely distinguishable from black beech. Rimu is the only podocarp present in quantity, save for the ubiquitous Hall's totara. Matai and kahikatea occur rarely on the valley floors and a few kaikawaka are present in high altitude bogs.
Red beech is the usual dominant on the moister sites, on slopes of cool aspect, on the river flats, in deep gullies, etc., though on such sites, wherever frost hollows exist or where the water-table is high, silver beech assumes dominance. Silver beech is also dominant on the upper slopes and ridge crests except where these are very dry. Throughout the forest red beech is normally sub-dominant on silver beech sites and silver beech is sub-dominant on red beech sites. Hard beech stands are characteristic of all dry slopes of warm aspect and of the lower dry ridge crests. At its extreme southerly limits hard beech occupies small local sites on west-facing slopes and the hard beech stands are entirely surrounded by red beech/silver beech stands. Mountain beech occurs as a riparian species down all streams draining from high flat ridge crests on which are found mosaic stands variously of mountain beech, red beech and silver beech, or mixed stands of these species. Where drainage is impeded, mountain and silver beech form stunted communities occasionally containing kaikawaka, bog pine or pink pine.
Rimu occur mainly on the lower slopes to the north, in association with red beech. Locally there may be up to eight rimu per acre but this figure is exceptional and the average would be three to four. The individual rimu are of medium size and appear healthy and vigorous. Seedlings, though never abundant, can be found in appreciable numbers but healthy vigorous saplings are greatly outnumbered by the old trees.
Wendelken, on the basis of field studies, concluded that rimu was, in these stands, a relict species, “… the southerly limits of the species are shifting bodily northwards”. Hard beech, also, now exists on certain sites where environmental conditions are markedly unfavourable. “In its upper limits there is virtually no regeneration of hard beech and this under a relatively
open canopy permitting more than an average amount of light to reach the forest floor. The dense sapling and pole growth at its lower levels give the impression that, as a type, the hard beech stands are moving bodily down hill in search of warmer conditions not sufficiently moist to allow competitive growth of red or silver beech. But these latter species are able effectively to cheek this downward movement because of the limiting factor of temperature which is operative over wider areas than in the past.”
In other words, hard beech is in process of being pinched out along the mid-slopes of warm aspect. Silver beech and red beech invade and occupy hard beech sites on the upper slopes consequent on the failure of hard beech to regenerate but red beech and silver beech yield no ground to hard beech on the lower slopes and valley floors. It is worth noting, at the same time, that red beech × hard beech hybrids were found with greatest frequency on sites where there was a trend toward elimination of hard beech.
The red beech stands of the lower slopes and valley floors appear stable but … “At higher altitudes the red beech stands are deteriorating.” Mountain beech on the higher ground to the south “… is proving an active invader”. It has spread down the streams and rivers apparently hybridizing with and swamping out the residual black beech giving a tree with the general appearance of mountain beech but with “… the timber qualities of black beech and a site tolerance and vigour intermediate between the two”. A gradual spread of trees of this type from riparian sites across the river flats and through the red beech stands of the lower slopes to the dry ridges where hard beech stands are stagnating, is traceable. At the same time, “There remains in the south and around the margins of the forest a more typical mountain beech type which shows a vigour surpassing that of the other beech species ”.
In the south some 5,500 acres of forest were wind-thrown in approximately 1870. To-day, pure stands of mountain beech now exist on sites where the old forest was of red beech, the fallen red beech logs still lying on the ground. On slightly lower slopes the young stands show silver beech and mountain beech co-dominant where previously red beech was dominant. Red beech pole stands developed following the wind-throw only on the warmest sites on moist but well drained slopes. On such sites red beech saplings and poles out-grow and suppress the other species, the reverse holding true for all other sites.
Wendelken's final conclusion was that, “The overall pattern indicates that a warmer and moister climate was operative in the area some time in the past.” Re-adjustments of species to sites, under the new climates, are as yet incomplete. A clear comprehension of this position is the only foundation upon which successful management of the forest could be based.
The Forests Of Eastern Marlborough
No recent field studies have been made of the forests of the Marlborough Sounds region. With respect to the forests of Eastern Marlborough, however, the main elements of forest type distribution are straightforward even though they lead, on the ground, to the development of a most intricate forest type mosaic.
As a consequence of the easterly trend of the main divide northwards from the Lewis Pass, dry inland ‘sub-continental’ climates are displaced toward the coast, a displacement accentuated by the presence of the Inland and Seaward
Kaikoura Ranges which lie parallel to the main divide and between it and the sea. There is consequent compression of all the various forest types as described for Canterbury, the various matai/totara/kahikatea types and their scrub hardwood derivatives, and the various beech forest types of the foothills and main ranges, into a comparatively narrow strip of territory. And into this complex there is injected a strong temperate maritime forest element particularly along the coastal slopes of the Seaward Kaikoura Range. At the same time, many species, otherwise found only in the forests of the North Island, enter the stands, the most noteworthy of these northern species being tawa (Beilschmiedia tawa). Accordingly, it is not unusual to find, in close juxtaposition, such diverse types of forest as, for example, matai/totara/kahikatea stands, lowland podocarp/tawa forest, rimu-rata/kamahi stands, red beech or red beech/mountain beech stands, broadleaf, broadleaf/fuchsia or broadleaf/fuchsia/kowhai scrub forest types, plus various types of coastal forest, e g., ngaio (Myoporum laetum)/karaka (Corynocarpus laevigata) stands.
As would be anticipated from the occurrence in these forests of many northern species, coastal climates are mild. It might therefore be expected that the matai/totara/kahikatea stands would display a somewhat greater vigour than, for example, stands of these species as developed in Southland. The lowland forests of the Marlborough coast have, however, largely been cleared to farm and this point cannot now be demonstrated; but, where remnant stands of this type are still present on the foothills, the stands are in much the same general condition as those found far to the south. Thus, on Mt. Fyffe, the forest is largely scrub hardwood forest of the types typically developed following elimination of the podocarps, a few old matai, totara, kahikatea and rimu surviving particularly on the deeper colluvial soils around the base of the mountain. On higher slopes there are extensive stands of broadleaf/fuchsia forest with small interspersed stands of red beech. Mountain beech is present on lowland riparian sites and stunted Hall's totara occur toward the timber line.
Tawa is not found on Mt. Fyffe but occurs a few miles to the north, an occurrence first reported by Smith (1935). But before quoting Smith's account of this tawa stand it might be appropriate to cite Cockayne on the question (Cockayne, 1928, p. 167). According to Cockayne, “Frequently, but in the southern part of its range more especially, tawa forest comes into contact with Nothofagus forest, but the latter in general is confined to the more barren dry slopes or ridges, while tawa is in the gullies and on the rich alluvial soil of the flat ground”. That is the orthodox, the ‘text-book’ view; but Smith's description of the southernmost stand of tawa yet found reads as follows:—
“The situation of the colony presents some peculiar features, worthy of further investigation. The altitude is remarkable for such a southerly occurrence. In the more northerly forests of the South Island, the species is confined to coastal forest and probably seldom is found more than 400 ft. above sea-level (e.g., Pelorus Valley and Wangamoa Valley) Colonies do occur to about 800 to 900 ft. altitude but the species is certainly never there to be found in forest subject to snow-break, of which the Kaikoura forest in question shows obvious signs. The sequence of species from the valley bottom of the Aniseed (stream) is likewise worthy of record‥ The colony of tawa in question lies on the right side of the Aniseed Stream, i.e., it has a warm north-easterly exposure. The lower slopes of this north-east face carry
a magnificent stand of rimu forest, with occasional totara and kahikatea. Above this are small colonies of mountain beech, outliers, as it were, of the beech forest on the south-western aspects of the valley. Above this matai appears and totara and kahikatea increase in numbers until the forest has rimu, matai and totara as co-dominants, with quite numerous kahikatea interspersed. This belt, a very fine stand of milling timber now almost lost to the South Island, continues through perhaps 250 feet of altitude suddenly and without warning then giving place to the tawa colony. The occurrence of tawa at a higher level than mountain beech in any part of its range would be notable. To find such a sequence on the southern limit for the species is almost unseemly.”
On the contrary, such a sequence is precisely what would be expected at the southern limit for the species. The sequence described by Smith is a thoroughly normal reversal pattern with pockets of mountain beech infiltrating upwards through the podocarp stands from riparian seed sources, the tawa stands persisting on the ridge crest pending occupation of the site by mountain beech. Smith makes no note concerning the presence or absence of young podocarps, seedlings, saplings or poles. But in his remarks, “magnificent stand of rimu”, and, “very fine stand of milling timber”, it is perhaps, legitimate to read the implication that the podocarps are very large and consequently very old trees. There can, however, be full agreement with Smith's concluding statement, “The situation of the colony presents some peculiar features and is worthy of further investigation.”
The forests of the region as a whole are worthy of more detailed investigation and, without any doubt, such an investigation would throw additional light on the many processes of forest re-adjustment in response to regional climatic changes. It is, however, already quite clear that the main trends in forest evolution, in Marlborough, parallel those described for the forests of other South Island regions.
The Forests Of Fiordland
As already described, the forests to the south of the Haast River, South Westland, are red beech, silver beech, mountain beech forests, with coastal development of Westland type podocarp stands. The podocarp element steadily diminishes in importance from north to south and, by the time the Hollyford River is reached, distinct podocarp stands occur on local and specialised sites only. Rimu/rata/kamahi hill stands are found as far to the south as Martins Bay, where they occur on the western slopes of the Sarah and May Hills Matai/kahikatea/rimu stands are developed on the valley floor alluviums of the Hollyford Valley, e.g., near Lakes McKerrow and Alabaster. Rimu also occur scattered through the beech stands on the lower mountain slopes, and the mountain or silver beech stands of the upper slopes are locally replaced by rata/scrub-composite stands otherwise more typical of the Westland podocarp region.
The Hollyford River, however, marks the northern boundary of a distinct forest region, the Fiordland region, a rugged. deeply dissected, glacially eroded gneissic upland subject to torrential rain generally exceeding 200 inches per annum and locally exceeding 300 inches. Summarised accounts of the region, its climate, topography, geology, vegetation, forests and fauna, have recently
been made available (Poole, Ed., 1951). The present account details a few significant items from the forests only.
Silver beech is the universal dominant in the forests of the precipitous rock walls falling to the fiords and trough-like valleys, yielding place, locally only, to rata stands developed on the steepest cliffs. Rata and kamahi are present throughout the silver beech stands as sub-dominants and scattered stunted rimu occur in the forests of the fiord walls. These forests develop upon, and are rooted in, a heavy moss blanket which overlies the smooth ice polished rock. In the normal sense of the term, there is no soil at all. The moss blanket is perpetually saturated by seepage waters and, wherever these collect and stagnate, bog forest types develop irrespective of the angle of slope. In these types of bog forest, mountain beech is the usual dominant with pink pine, yellow-silver pine, bog pine, mountain toa-toa and manuka. Inland, the forests of the valley walls are generally similar, though without rimu. Stands of all these types are periodically devastated by immense land-slides and all stages in stand redevelopment are everywhere evident.
In the valleys, the valley floor forests may show rimu, rata and kamahi co-dominant near the heads of the fiords but, away from salt water, silver beech is the dominant species and the stands contain no rimu. Considerable sphagnum moss/sedge bogs and swamps are developed on level stretches of the valley floors. Rock bars (riegals) characteristically carry stunted stands of the bog forest type, and communities of kamahi, broadleaf and mountain ribbonwood occupy temporarily the debris of past land-slides.
To the east, where the boundary of the Fiordland region is marked by the great cold water lakes, Te Anau, Manapouri, Monowai, Hauroko and Poteriteri, mountain beech gradually replaces silver beech as the main dominant in the mountain forests, and rimu re-appear in the stands a few miles to the west of the lakes, kamahi/rata/rimu stands developing, locally, on stream and river deltas. To the east, also, yellow-silver pine and pink pine decrease in abundance and bog forest stands then consist of mountain beech, only, with a little bog pine or manuka.
This pattern of forest is generally constant over the whole of Fiordland though, in the extreme south-east, silver beech remains the usual dominant species. Red beech and matai, it will be noted, play no part in these forests. Red beech is found around the entire landward periphery of the Fiordland region, in the Hollyford and Eglinton Valleys, in Dunton Forest and near Lake Manapouri, with small relict stands, already described, south to Lake Monowai and the Lillburn Valley. And the distribution of matai parallels that of red beech very closely. There are unconfirmed reports that both species do occur in the forests along the mid-western shores of Lake Te Anau, where the soils, locally, are derived from rocks other than the usual Fiordland gneiss; and a few red beech and matai may occur in the valleys about the head of Milford Sound, field notes taken in this area being washed out by rain.
The point to be stressed, however, is not the absence of these species from Fiordland but the fact that, along the whole landward boundary of Fiordland there exist stands, containing these two species, which are markedly abnormal in condition, distribution and behaviour, abnormalities explicable, as has been shown, only in terms of the theory that there has been, in the recent past, a
marked fall in regional temperatures accompanied, in certain instances, by a fall in effective precipitation.
But the main Fiordland forests contain little to support this theory. Few changes in species distribution appear to be in progress. The following items are, however, suggestive.
In the first place, the fiord head rata/kamahi/rimu stands are identical in condition with the rimu/rata/kamahi hill stands of Western Southland and of Westland, stands in which, as has been seen, rimu must be a relict species. Few seedling, sapling, or pole rimu are present in the Fiordland rimu/rata/kamahi stands and, in many places, these stands are actively invaded by silver beech. And the rimu of the fiord walls, also, leave an impression of general overmaturity despite their typically stunted stature. Some younger trees are present, but these appear out-numbered by stag-headed veterans.
Secondly, many of the rata stands of the fiord and valley walls are very old stands containing, for such sites, very large trees, but where rata stands have developed more recently on land-slide scars, growth appears to stop when individual rata are little more than large shrubs. The old trees are single trunked, but the young trees are multi-leadered. This, again, is in impression only for, on these precipices, sites conditions do not favour detailed study of growth forms; but it is distinctly possible that climatic conditions no longer permit the growth of rata to the stature previously attained.
Thirdly, the timber line on the western fall of the Fiordland mountains is excessively irregular. Island stands of silver beech occur above the timber line proper, and tongues of sub-alpine scrub or tussock grassland thrust downward into he forest. In these silver beech islands the trees are frequently all old and massive, and though the absence of younger stems may be attributable to recent browsing by introduced mammals, such browsing does not explain the occasional presence of old stump and log mounds on sites now given over wholly to al line meadows. Beech forest timber lines are normally very regular, but the western timber lines on the Fiordland mountains, together with those of the Paparoa Range far to the north, diverge sufficiently from the normal to demand explanation. And in both cases the suggestion is that these timber lines are falling.
Fourthly, true totara has yet to be found in the Fiordland forests. Hall's totara, as usual, is present throughout, though most individuals are little more than large shrubs. A few trees of larger diameter, however, occur near the beaches at the heads of several of the fiords, and these are not directly referable to either Hall's totara or to true totara, but have the bark of the former and, the needle of the latter. They may be hybrids, though they are, if so, of remarkably constant form. On the other hand, however, in the valley of the Rugged Burn, which drains eastwards to the middle fiord of Lake Te Anau, a few very long, fallen logs, heartwood only, have been discovered, the discovery of similar logs in the Longwood Range forests being followed subsequently by the discovery of a relict stand of true totara.
These are all minor points, but the minor points add up. There is nothing yet discovered in the Fiordland forests to establish, beyond doubt, that there has teen a recent fall in regional temperature; but there are likewise no items at variance with this hypothesis. With respect to rainfall, it would be difficult to imagine wetter conditions than those usual in Fiordland to-day. Annual
rainfall may once have been heavier, but an additional 50 or even an additional 100 inches per annum might make little difference to the forests, which would remain stable under any rainfall sufficient to prevent the drying out of the moss blanket in which the stands are rooted. With falling temperatures this becomes the more certain even though rainfall totals may have fallen. Therefore, the suggestion is that effective precipitation is now, if anything, greater than it was in the past and such a conclusion receives some support when the silver beech stands of the great valley head cirque floors are examined. With respect to several such stands there has been an apparent increase in swampiness with large, dead, or unhealthy silver beech standing, so to speak, with their feet in the water. Young silver beech. in such cases, are wanting.
Recent changes in these Fiordland forests cannot have been strongly marked. Probably these has been little more than a gradual diminution in the number of rimu in the stands of the fiord walls, a squeezing out of all former small, valley floor podocarp stands, a slow fall in the regional timber line, and a general decrease in the vigour of all species as limiting conditions for tree growth are closely approached.
One last point Fiordland, to-day, is without glaciers with the exception of those on the higher ranges, notably on the Darran Mts., in the region of Milford Sound. To the south of Milford Sound there are few permanent snow-beds, but, even so, limiting conditions for forest growth are closely approached. Continued existence of forests in Fiordland throughout a glacial epoch is inconceivable. But silver and mountain beech stands, to-day, occupy all sites, including even the most remote Fiordland valleys separated from the main forest mass by high and barren mountain summits. In Westland, on the other hand and as already described, the beech species have not yet migrated hack on to favourable sites though migration routes lie over country posing far fewer obstacles to species migration than are to be found in Fiordland. The obvious conclusion would appear to be that Fiordland was little affected by the last major glacial advance which must, therefore, have been restricted, in the main, to regions flanking the highest central portion of the Southern Alps, to areas corresponding, in other words, to the Westland podocarp region and to the region characterised, in the east, by widespread occurrence of Hall's totara/kaikawaka and derivative forest types. In other regions, in Fiordland and in Western Nelson for example, forest evidence would suggest that the last glacial epoch was marked by little more than the development or extension of valley glaciers with extensive beech forests remaining on the lower ground.
If this was the case, then analyses of species distributions interpreted in the light of compound Pleistocene snow lines, such as those advanced by Willett (loc. cit.), are of little real use, for no allowance can be made therein for the measure of control of species distribution still exercised by the events of the inter-glacials, nor can any allowance be made in respect to the changing incidence of heavy glaciation from one ice advance to the next.
But this is a digression for the moment the main point to note is that the forests of Fiordland. in type and in condition, reflect mainly present environmental factors, though slow changes may be in progress consequent on a recent fall in regional temperature. The evidence for such a fall comes, however, not from study of the Fiordland forests but from study of adjacent forests to the east and to the north.
General Discussion of the Facts and Hypotheses.
Concerning The Prominence Of Mal-Adjustment Features In South Island Forests
It has been shown that the indigenous forests of the South Island are in a condition of essential mal-adjustment with respect to present climates. The condition is sometimes profound, sometimes slight, varying from region to region and from forest type to forest type; but, in all regions and in most forest types, some indication is obtainable of this lack of balance between forests and climates.
It has also been shown that this state of affairs dates back, in all probability, to climatic changes experienced during the 13th century A.D., or thereabouts, and this variation in climate probably occurred synchronously with major climatic changes known to have taken place in the northern hemisphere. Why, therefore are the after-effects of these climatic variations so evident a feature of South Island forests when not perceptible to an equivalent degree, or so a perusal of forest literature would suggest, in European or in North American forests?
Several strong reasons may be advanced and, collectively, they amount to this, namely, that South Island forests are virtually laboratory forests for the study of such phenomena.
In many forest regions of the world, the processes of forest re-adjustment in response to climatic variations must be entirely masked or over-ridden by changes consequential on the activities of men or of animals. Thus Kalela (1949), discussing the forests of Finland, writes, “The present composition of tree species in the Finnish forests is a result, primarily, of forest fires that have raged through all time, and of the primitive method of agriculture in general practice until the beginning of the 20th century … cultivation by burning over … even if, more recently, cuttings in particular have added many new features to their character.” And in England, to cite an extreme example, it would be most difficult to find, in any forest, more than a trace of indisputably primitive vegetation unmodified by the acts of man and of his animals. But even in Europe, though locally only, the consequences of 13th century climatic disturbances are discernible. Thus, “… woods with abundant beech trees covered the Riesengebirge right up to the ridges of the mountains, at least until the beginning of the 14th century. From the 14th to the 17th centuries the upper tree line lay 100–200 metres lower than either before or after.” (Steensberg, 1951.)
In New Zealand, however, the aboriginal inhabitants were a people possessing but a stone age culture, and even they had been in occupation of the land for little more than 1,000 years prior to the advent of European settlers. The Polynesians, moreover, were typically food gatherers and hunters and, as such, left little mark on the forests as a whole. They were responsible, at least in part, for the destruction by fire of the ancient podocarp forests of eastern regions of the South Island, but, even here, some forest escaped burning, sufficient stands remaining intact to permit reconstruction of a clear picture of the forests as they once must have been.
Re-inforcing this comparative freedom of the forests from cultural interference was their complete freedom from grazing and browsing mammals. Up to the period of the mid-18th century, the only mammals present were the Polynesian introduced dog and rat. The physical factors of site and climate were, therefore, the decisive factors controlling the distribution of forest species and forest types. The great variables of human and of animal activity were largely eliminated, leaving but the one great variable, climate, to be studied; and the effects of climatic variation will, therefore, be more readily recognisable than would otherwise have been the case.
Turning now to the climate itself, it might be noted that, as fully demonstrated by Garnier (1950), the South Island of New Zealand is marked by intense climatic regionalism. Regional climates of to-day vary from warm temperate maritime climates to the extremes of regions carrying permanent ice and snow, from semi-arid grassland climates to super-humid cool to cold temperate forest climates. This regional diversity is a consequence both of the geographical position of the land mass with its major axis extending for 500 miles from north to south across the path of the westerly winds, and of topography with high mountain barriers paralleling the western coasts and expanding out to form extensive highlands both in the far north and in the far south. Bach climatic region so developed is strictly limited in area so that no portion of any regional forest is far removed from the inter-regional climatic transition zones. The forests, throughout their full extent, may, in fact, be regarded as transition zone forests, as ecotonal forests; and over their full extent are developed those phenomena which, in the forests of continental land masses, are typical of the transition zone forests only.
At the same time, the climatic changes actually experienced also varied from region to region. The initiating change, the fall in mean or effective temperature, must have been common to all regions but the consequential changes, particularly in respect to wind frequencies, force and direction, and therefore in respect to regional precipitation effectiveness, varied greatly in degree and possibly also in direction. The behaviour of the forests under widely varying conditions and degrees of climatic change can, therefore, be studied. Seldom will laboratory conditions be so nearly approached in the study of biological phenomena in the field.
Finally, two separate factors tend, in South Island forests, to highlight the mechanisms of forest re-adjustment in response to regional climatic variations. These are, firstly, the methods of species migration for the in-coming beech species with production of characteristic and unmistakeable migration patterns and, secondly, the extreme longevity of the out-going podocarp species. If the seed of the in-coming species had been bird distributed, or if the out-going species were short life species, then all processes of forest re-adjustment would have been further advanced toward completion and would have been far less distinct and regular.
All these several factors, the comparative freedom of the forests from all forms of cultural interference and from the impact of animal grazing and browsing, the general prevalence of ecotonal conditions consequent on marked climatic regionalism, and the behavioural idiosyncrasies of the beech species on the one hand and of the podocarp species on the other, in combination, are responsible for the prominence of mal-adjustment features, in respect to present climates,
evident in the forests of the South Island. The forests of few world regions can be expected to display, with equal clarity, the many phenomena of change.
That these phenomena are, however, by no means peculiar to New Zealand forests is evident from the reports of the Finnish (1937–38) Expedition to Patagonia (Kalela, 1941). In eastern Patagonia present climates closely parallel those characteristic of eastern regions of the South Island of New Zealand; and the forests, also, are similar in type, beech forests with podocarps and Libocedrus in New Zealand and beech forests with Fitzroya, Saxegothea, Araucaria and Libocedrus in Patagonia. Kalela, in his report on the Patagonian forests deals with, inter alia, “The westward retreat of the forests before the advancing steppe, and associated changes in the specific composition of the forests, phenomena ascribed chiefly to a deteriorating climate.” This abstract (Kalela, 1950) summarising the reports of the Finnish Expedition would serve equally is well as a summary of this present report on South Island forests.
There are, of course, many differences in detail. Thus in New Zealand, the beech species. principally mountain beech, withstand drier conditions than do any of the podocarps; but, in Patagonia, Araucaria (and occasionally Libocedrus also) persists long after increasing desiccation has lead to the final elimination of the beech species. “Finally Nothofagus antarctica disappears and we are left with a broken up Araucaria zone, the stands becoming more and more group-like and stunted in growth amidst the steppe. As these outposts fail to regenerate we find only the stumps left in the middle of the steppe”. But, as in New Zealand, so also in Patagonia, there is in evidence a considerable interchange and re-distribution of species even where the forest cover remains intact “The change to drier conditions in the region first become noticeable in the N. procera stands. Many dead tops appear and the stands shrink in size; N. dombeyi invades the old N. procera sites and becomes the dominant species. Soon a wedge appears between the N. dombeyi and N. pumilio belts and this is invaded by N. obliqua, first in mixture but later becoming more and more dominant and later tending to form pure stands.” These Patagonian forest re-adjustment processes compare very closely with those described in this report for the forest of Big Bush in Central Nelson.
One last example might be quoted from Kalela's report. “In the far eastern parts of its range the N. dombeyi stands are also invaded by N. obliqua from the east. N. obliqua thus advances both from the east and from the west and finally takes over the entire N. dombeyi area, forming fairly pure stands. Only on south facing slopes is N. dombeyi still dominant … In a further stage toward more and conditions, N. antarctica and Libocedrus invade the N. obliqua stands.” Again a development closely paralleling those found in many South Island forests.
In Patagonia there would appear to have been no equivalent to the old eastern matai/totara/kahikatea forests of the South Island of New Zealand. The Nothofagus/Araucaria/Libocedrus forests described by Kalela are the counterparts of the beech forests (with scattered podocarps) of, for example, the Canterbury foothills. New Zealand conditions would seem to be more closely matched in Tierra del Fuego. To quote Kalela's summation of the results of the 1927–28 Finnish Expedition, “As far as could be ascertained by this Expedition, the period shortly after the glacial epoch was marked by an active advance of the forests from the Pacific coast toward the Atlantic coast,
Later, in fairly recent times, the climate changed and with the deterioration in conditions the forests retreated from. the Atlantic coast toward the mountains in the west. The initial advance of the forests was attributed to a warmer climate than the present causing the air to rise higher while travelling east leading to a higher rainfall over the far eastern parts of Tierra del Fuego.” But, “In Patagonia, however, the forests seem to have withdrawn continually from east to west. After the glacial epoch there never existed any forests worth mentioning”… i.e., over the greater part of the eastern Patagonian plains now under steppe… “and the warmer climate failed to cause any general eastward advance of the forests. The climate at that time was characterised by a dry warm phase and was very windy. The sub-tropical high pressures were then lying farther to the south.”
In the South Island of New Zealand, the post-glacial period was marked, at least in its later stages, by occupation of the greater part of the eastern plains and foothills by matai/totara/kahikatea forests, by occupation of much of the mountain country by Hall's totara/Libocedrus forests, and by survival or development of beech forests on a variety of sites but mainly at high altitudes. This was a period of warm humid climate with, as in Tierra del Fuego, higher precipitation effectiveness than at present over eastern regions. Then, comparatively recently, following the onset of an era of colder and drier climate, the podocarp forests stagnated and were, in part, burnt, the beech forests locally and temporarily advancing but later, in many places, retreating before the advancing tussock grasslands. And as described for the Patagonian forests by Kalela, there has been a concomitant multiple interchange and re-distribution of forest species.
Kalela did not observe any lowering of the timber lines in Patagonia but he quotes other sources to the effect that climatic conditions in Chile for forests at the timber line have deteriorated. In the South Island of New Zealand, though there is some evidence to hand suggestive of timber line instability in regions to the east of the Southern Alps, these phenomena are everywhere more strongly marked to the west of the main ranges, regionally corresponding to the Chilean slopes of the Andes. It would appear to be logical to anticipate as close a degree of parallelism between events in progress in the forests of southern Chile and those in progress in western regions of the South Island as has been demonstrated for the forests of eastern districts and the forests of eastern Patagonia and Tierra del Fuego.
In Western Tasmania, Casson (1952), found some evidence suggestive of the fact that “the whole flora of the region may be in a dynamic state … that recent climatic changes may not yet be fully reflected in the existing vegetation.” Here, again, a species of Nothofagus is involved, N. cunninghamii apparently, over wide areas, invading and replacing mature or over-mature stands of eucalypts. And, somewhat further afield, comparable phenomena have been described from tropical Africa King (1953), states that Aubreville “… believes that formations which might be described as palaeochmaxes imperfectly adjusted to the climate of to-day are very widespread.” Many hygrophilous forests now existing in regions characterised by long dry seasons are thought to survive more or less precariously from periods of more humid climate and the ease with which such forests are entirely destroyed by fire is thought to be in direct reflection of this, an argument already advanced in this
present report in explanation of the virtual complete destruction of the old matai/totara/kahikatea forests of the South Island.
In respect of their features of instability and change, therefore, the forests of the South Island of New Zealand are by no means unique; but these features are here so strongly developed that they must govern and control all acts and techniques of forest management. To paraphrase a remark of Kalela's natural developments in forest type evolution may, by various silvicultural methods, be either expedited or retarded; but their course cannot be changed. The facile notion, frequently advanced, that the indigenous forests of New Zealand have developed in complete and entire harmony with local environments, is demonstrably erroneous. And all derivative arguments are equally false, for example, the argument that principal reliance for future timber production should be placed on the ‘natural’ indigenous forests rather than on the ‘unnatural’ forests of exotic species, or the argument that, in the field of watershed protection, it will be wholly sufficient to shield the ‘natural’ forests against fire and against browsing animals, leaving the rest to ‘nature.’ Can the climatic clock ever be set back?
Some Implications And Research Requirements.
That this present account of the indigenous forests of the South Island is a speculative one is readily admitted No clear proof of the fact of climatic change can yet be adduced; but, likewise, there is no proof of long continued climatic stability. If such stability be assumed, the forest story at once disintegrates into an incoherent and incomprehensible jumble of miscellaneous facts wherein can be discerned no clue that might lead to any substantial advance in the field of practical forest management It is in this that the strength of the present account rests. It does provide an intelligible framework into which can be woven the facts as known and which is strongly suggestive of further lines of enquiry. It does serve in explanation of past successes and failures as known to practising foresters.
An almost overwhelming volume of detailed investigative and patient experimental work remains to be undertaken. In fact, it might well be said that each section or paragraph of this report is, essentially, little more than an outline of a research project for the future. Proof or disproof of the basic hypothesis, that of recent climatic change, is not a problem for foresters working alone. A very considerable measure of assistance will be required from pedologists, palynologists, glaciologists and other specialists. Radio-active (C-14) carbon methods for dating organic materials will obviously be of immediate practical value and it should be possible to obtain reasonably precise dates for the ‘Fires of Tamatea’ which destroyed the old podocarp forests of eastern regions. Similarly, the initiation of more intensive studies of historical river regimes would prove of great practical value in so far as such studies will throw light on the climatic vagaries of the past.
In the glaciers of the South Island we have, of course, a ready instrument at hand for the measurement of current climatic fluctuations but the climatic record of the past provided by the glaciers will not be an easy one to read. This will particularly be the case with respect to comparatively minor climatic fluctuations of the type recently (and hypothetically) experienced. When climates become both colder and drier, and when there is considerable local
and regional variation in the intensity of climatic change, the behaviour of individual alpine glaciers will frequently be idiosyncratic. But although the record of past climatic disturbances as recorded by the glaciers will not be easy to interpret, glaciological studies are essential to our understanding of present trends.
In this report on forests and climates, we have been concerned with analyses of the after-effects of climatic changes thought to have been experienced some 800 years ago. Where forest re-adjustments are not speeded by human or animal agency, this considerable time-lag must be thoroughly normal. Re-adjustments in response to one particular change in climate may still be in progress when the next change occurs Theoretically, they may even, in fact, continue through the early years of a subsequent climatic period. Thus, for example, the forests may still be responding to the onset of an era of desiccation for some considerable time after climates have again tended to become wetter. When it is said, therefore, that the forests of the South Island are in active process of change in response to climatic deterioration with onset of colder and drier conditions, it is not implied that climates are still becoming colder and drier. We may, indeed, have already entered a new climatic era. This is a possibility wholly in line with recent developments in the northern hemisphere.
The eastern glaciers of the South Island are, at the moment, in general and rapid retreat, or show signs of rapid vertical wastage (Suggate, 1950). This retreat may be in continuation of trends of long standing; it may be consequent on the drier conditions that have obtained over the past several centuries; but it could be due to some far more recent rise in mean regional temperature. In other words, are climates now becoming warmer once again? And, if so, warmer and drier or warmer and wetter?
These questions are obviously of no small importance. In no field of practical endeavour will they be of greater importance than in the field of indigenous forest management. Future generations of New Zealanders may well witness a return to an era of podocarp favourable climate. At the moment, however, the tide of events runs strongly hostile to serious attempts, for example, to manage for long-term sustained yield timber production the commercially valuable podocarp forests though this tide may, in the distant future, turn. The important thing that must be recognised is the existence of these ‘climatic tides’ over which we have no control. Forest or range land policies prepared in ignorance of them must inevitably, in the long run, fail.
Present trends, over wide areas, lead to the replacement of valuable timber species by weed species, to serious difficulties with respect to the maintenance of important watershed protection forests, and to equally grave difficulties in the field of tussock grassland management (Raeside, 1953). These are facts, however unwelcome they may be. The problems they present will not be solved by failure to recognise their existence.
It might be said that we have been unlucky, just as the foresters of the Ozark Highlands, United States of America, have been lucky. In the Ozarks (Beilmann and Brenner. 1951 a and b) much of the land which is now under forest was, in historical times, grassland. These grasslands apparently existed within a region possessed latterly of a true forest climate, the forests being prevented from developing by re-current Indian fires. Following European
settlement of the land and cessation of burning, the land, to use the authors' expressive term, has ‘erupted into forest.’ And there is a rapid replacement of the more valueless species by the more valuable. Forest policies and forest management techniques designed for the Ozark forests will clearly be inapplicable in New Zealand. Policies and techniques for New Zealand forests must be founded in knowledge of New Zealand trends, not adopted or adapted from the policies or techniques of any other country. We must conduct our own research.
It would be fatally easy to extend and continue, indefinitely, this discussion concerning the implications of the hypothesis of recent climatic change, debating the influence of climatic variation on problems of plant speciation and hybridisation, on the processes of soil formation, on land forms, on Polynesian and European land settlement patterns, and on the whole range of wild-life problems with which we, in New Zealand, are faced. The net could be cast very wide but, in so far as has been possible, the discussion has been restricted to the field of forestry. New Zealand wild-life problems, problems intimately and inseparably related to forest problems, have been discussed by many workers, the latest treatment being that of Murphy (1951). One question, only, might here be asked. Can New Zealand wild-life problems be solved, or can they even be propounded satisfactorily, without a detailed knowledge of that extraordinarily complex and fluid environment into which so many species of alien animals were introduced? It would appear most improbable. The successful solution of current wild-life problems would appear to be entirely dependent on acquisition of a more thorough and comprehensive knowledge of past climates and of present climatic and vegetational trends.
But these and other matters must remain for future debate. The field of enquiry is so great, and the implications inherent in the hypothesis of climatic variation and instability are so many and of such importance, that it is not possible to do more, for the moment, than to declare the debate open. Much more information is hidden in the forests, information to be gained by more laborious and detailed study than anything attempted to date. As already stated, all that has been attempted in this report has been the tentative exposition of ideas gained during the course of a primary and incomplete survey of the forests For proof or disproof we must look to workers in other fields of enquiry.
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Barker, M. A., 1950. Station Life in New Zealand. 2nd. Ed., p. 117. Whitcombe & Tombs. London and Wellington. 237 pp.
Beilman, A. P., and Brenner, L. G., 1951a. The Recent Intrusion of Forests in the Ozarks. Ann. Missouri Bot. Garden 38: 261–282.
— 1951b. The Changing Forest Flora of the Ozarks. Ann. Missouri Bot Garden 38: 283–291.
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Casson, P. B., 1952. The Forests of Western Tasmania. p. 80 Journ. Inst. For Australia 16. (2) 71–86.
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Glossary of Plant Names Used
Podocarps And Other Coniferous Species
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Kauri||Agathis australis Salisb.|
|Kahikatea||Podocarpus dacrydioides A. Rich.|
|Kaikawaka||Libocedrus bidwillii Hook f.|
|Matai||Podocarpus spicatus R. Br.|
|Miro||Podocarpus ferrugineus D. Don.|
|Rimu||Dacrydium cupressinum Soland.|
|Totara (true)||Podocarpus totara D. Don.|
|Totara (Hall's)||Podocarpus hallii T. Kirk.|
|Bog pine.||Dacrydium bidwillii Hook. f.|
|Mountain toa-toa||Phyllocladus alpinus Hook. f.|
|Pink pine||Dacrydium biforme Pilger.|
|Pygmy pine||Dacrydium laxifolium Hook. f.|
|Silver pine||Dacrydium colensoi Hook.|
|Snow totara||Podocarpus nivalis Hook.|
|Yellow-silver pine||Dacrydium intermedium T. Kirk.|
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Black beech||Nothofagus solanderi Oerst.|
|Hard beech||Nothofagus truncata Ckn.|
|Mountain beech||Nothofagus cliffortioides Oerst.|
|Red beech||Nothofagus fusca Oerst.|
|Silver beech||Nothofagus menziesii Oerst.|
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Broadleaf||Griselinia littoralis Raoul.|
|Cabbage tree||Cordyline australis Hook. f.|
|Fuchsia||Fuchsia excorticata Linn. f.|
|Kamahi||Weinmannia racemosa Linn. f.|
|Kanuka||Leptospermum ericoides A. Rich.|
|Karaka||Corynocarpus laevigata Forst.|
|Kaikomako||Pennantia corymbosa Forst.|
|Kowhai||Sophora microphylla Ait|
|Kumara||Ipomoea batatas Lamk.|
|Mahoe||Melicytus ramiflorus Forst.|
|Manuka||Leptospermum scoparium Forst.|
|Milk tree||Paratrophis microphylla Ckn.|
|Ngaio||Myoporum laetum Forst.|
|Pigeonwood||Hedycarya arborea Forst.|
|Pokaka||Elaeocarpus hookerianus Raoul.|
|Pukatea||Laurclia novae-zelandiae A Cunn.|
|Rata||Metrosideros umbellata Cav.|
|Rata, northern||Metrosideros robusta A. Cunn.|
|Riboonwood, lowland||Plagianthus betulinus A. Cunn.|
|Ribbonwood, mountain||Gaya lyallii var. ribifolia Baker (Ckn).|
|Tawa||Beilschmiedia tawa Benth. & Hook. f.|