Art. XXIX.—Notes on the Plant-covering of the Breaksea Islands, Stewart Island.
[Read before the Otago Institute, 7th September, 1915.]
The Breaksea Islands consist of a group of six small islands lying on the east of Stewart Island, between Port Adventure and Lord's River Their latitude is 47° 6′ S. and longitude 168° 15′ E. As the eastern coast of Stewart Island trends away towards the south-west from this latitude, these islands receive no protection from the southerly weather, which strikes and breaks on their southern sides with full force; hence the name of the group. On the 7th January, 1915, by the kindness of Mr. Henry Hansen, I had the good fortune to be able to visit the principal islands of the group, and take some notes of their plant-covering.
Comparatively little has been recorded of the botany of these outlying islands; therefore a short description of their plant associations may be of interest.
Rukawaha-Kura, or Joss's Island.
This is the largest of the group, and lies only about 500 m from the mainland of Stewart Island It was the first one visited by me, and some time was spent in examining its vegetation The island is almost circular in shape. It is not more than about 50 m high, and is about 500 m. in diameter in its widest part. There is a good landing on the north-east side
The plant formations are best considered under three heads—namely, (1) rocks and cliffs; (2) forest; (3) heath
(1.) Rocks and Cliffs.
Most of the coast-line of the island consists of steep rocky faces, covered from above high-water level with a close association of almost pure Olearia angustifolia where there is sufficient soil to give it a hold, but in other places with Poa Astoni, which covers the cliff-faces with a grey-green drapery Here and there, where the wind strikes less directly, great green patches of Stilbocarpa Lyalln, with their large leaves overlapping one another, can be seen, giving quite a tropical appearance to the vegetation. On exposed rocks Crassula moschata is plentiful, its reddish stems contrasting strongly with the greyish-white of the granitic rock. At the rear of the frontal rocks the shore ferns Asplenum obtusatum and Blechnum durum are abundant, the former in more or less isolated clumps and the latter in large closely matted patches On the cliff-faces Olearia Colensoi is plentiful, especially behind the fringe of O. angustifolia; while Veronica elliptica, although a little past full flowering, still gave by its bloom a whitish tinge to the cliff-side, especially where the soil is deepest Occasionally Dracophyllum longifolium pushes its brown head through the other plants, especially where the stunted shrubs bear testimony to the power of the wind In parts of the island the cliff vegetation also contained Mesembiyanthemum australe and Tetragonia trigyna, both plants giving a warm colour to the association, the former by its bright-pink flowers and the latter by its reddish leaves when exposed to extreme light At a short distance away, however, the most dominant feature of the sloping cliff-covering is Olearia angustifolia, which is the principal plant in exposed situations. It protects
its close relation O. Colensoi from the devastating effect of the salt-laden wind. The steep rocky faces are, on the other hand, covered with Poa Astoni, while here and there in the crevices Veronica elliptica ekes out a precarious existence. On the south side of the island the principal plant near the water's edge is Olearia angustifolia, but as we get farther in from the shore on the steep face O. Colensoi is found, with an occasional Senecio rotundifolius and Dracophyllum longifolium. At an elevation of about 40 m. above sea-level there is an open heath on this side, which is dealt with under its appropriate heading.
When approaching the islands the physiognomy of the forest nearest the coast presents a greenish-grey appearance The roof is close, and its wind-shorn appearance bears testimony to the severe gales which characterize this region. This fringe is composed almost wholly of Olearia angustifolia and O. Colensoi. A little farther back isolated patches of bright green attest the presence of Griselinia littoralis, while on the summit of the island dark patches of Metrosideros lucida are visible. Upon a closer acquaintance it is found that the soil consists of a deep layer of peat, fairly dry, and honeycombed in all directions with the burrows of mutton-birds (Puffinus griseus). There can be little doubt of the effect these birds produce on the vegetation. Not only do their tracks ramify in all directions, showing the physical effect of their traffic, but their manure is everywhere in evidence, while their burrows must greatly assist in the quick drainage of the surface, and also help to aerate the soil and make it suitable for plant-growth. The forest proper is chiefly Metrosideros lucida, which is not more than from 8 m. to 10 m. high, and consists of excessively gnarled trunks, usually prostrate for part of their length, and then turning their close twiggy tops upwards. Growing among these trees, and frequently epiphytic upon them, one finds Griselinia littoralis, Pittosporum Colensoi, Nothopanax Colensoi, Coprosma areolata, Fuchsia excorticata, Rapanea Urvillei, and Olearia Colensoi, with occasional plants of Aristotelia racemosa, Olearia arborescens, Coprosma foetidissima, and Nothopanax Edgerleyi. Here and there the tree-fern Dicksonia squarrosa grows in clumps, but is nowhere plentiful.
The most marked feature of the undergrowth is the strong growth of Stilbocarpa Lyallii, which practically covers the whole forest-floor. It is very luxuriant, and in several places is over 1–5 m. high. The leaves from actual measurement, attain occasionally the great width of 63 cm. This plant forms in most parts great continuous growths, acres in extent, and in some places it is difficult to get through. Its great leaves, spreading horizontally, exclude the light, and prevent other growth on the peat, which is frequently so pierced by the mutton-bird burrows as to sink under one's steps. Where sufficient open space allows, strong clumps of the ferns Asplenium lucidum, A obtusatum, and A. scleroprium will be found. The last-named fern grows particularly strongly in several places where it is undermined by burrows. In these places the ferns often have a distinct caudex, and stand nearly 1–5 m. high.
Patches of Polystichum vestitum are also occasionally seen, together with patches of Histiopteris incisa. The tree-trunks are covered with Polypodium diversifolium and Asplenium flaccidum. In several instances Olearia Colensoi had a trunk nearly 75 cm. in diameter near the base, but quickly branched into several strong-growing limbs which ultimately reached a height of nearly 10 m. Near the edge of the cliff—and, in fact, in most places where the
strong light can reach the soil—clumps of Poa foliosa are common, and in open places this becomes a thick mantle, under which the mutton-birds burrow for nesting purposes. I also noted Rubus australis, but it is not very common. Here and there Dracophyllum longifolium grew in the forest, but was not plentiful in this association. Along some of the open tracks I also noted the following small plants: Carex lucida, Plantago Raoulii, Cardamine heterophylla, Blechnum durum, B capense; and the orchids Pterostylis australis, Thelymitra uniflora, T. longifolia, Caladenia bifolia, Microtis unifolia, and Prasophyllum Colensoi. In damp places Carex trifida is not uncommon, and I noted one or two specimens of Carex lucida.
On the south side of this island, where the full force of the prevailing wind and sea strikes the coast, there is a considerable area of open heath. This is on one of the highest parts of the island, and presents a somewhat bleak appearance. The general aspect is as if fire had run over the ground, the dead branches of the low scrub being bleached and white. I do not think, however, that fire has ever touched the island, the dry appearance being a characteristic result of the stormy conditions. The soil is peaty and in parts fairly damp, but could hardly be called boggy. The plant association of this part is very similar to that found in exposed places on some of the mountain peaty heaths in Otago where the water-content is not high. Low stunted Leptospermum scoparium forms the principal shrubby vegetation in the most exposed parts, the shrubs being fairly open. Dracophyllum longifolium is the next most conspicuous plant among the shrubby vegetation. These plants are dotted about everywhere, but do not attain more than about 1 m. in height, except in the hollow and sheltered places Here and there Styphelia acerosa and Olearia aiborescens are common, while between these plants Oreobolus pectinatus cushions are common. Red patches of Diosera spathulata are plentiful. I also noted one plant of Dacrydium biforme. In the drier places Lycopodium volubile was noted, together with patches of Gentiana saxosa Stunted Phormium Cookianum is also present in isolated bushes. Oreostylidium subulatum is not uncommon, while Anisotome intermedia (?) is also seen, together with Thelymitra uniflora, Pentachondia pumila, and Leptocarpus simplex. I also noted one patch of Neitera depressa. The southern coast of the island is steep, and is protected by the usual fringe of Olearia angustifolia, O Colensoi, Senecio rotundifolius, and Dracophyllum longifolium, while the shore ferns Asplenium obtusatum and Blechnum durum are common. There were no signs of bird-burrows on the heath, no doubt on account of the wetness it must experience in bad weather
(4) Introduced Plants.
Near the mutton-birders' huts, where a small clearing has been made, I noted the following introduced plants, all of them growing luxuriantly: Dactylis glomerata, Holcus lanatus, Rumex obtusifolius, R Acetosella, Stellaria media, Sonchus asper, Poa pratensis, and Trifolium repens. I also noted Cotula coronopifolia near the door of one of the huts, but, although this is an indigenous species, it had all the appearance of having been introduced. The above species have no doubt been accidentally introduced to these islands on the annual visits of the Maoris when mutton-birding. None of them have spread beyond the clearing.
Breaksea Island, or Whareotepuaitaha.
This island stands farthest out of the group, and consequently is in a much more exposed position. From a little distance it presents a remarkably grey uniform appearance, the tops of the trees being as close as possible and seeming as though trimmed. Upon landing on the north-west side the same shore association is met with as is mentioned above; but when the low forest is entered it is at once seen that much less undergrowth is visible, except along the north side, where it is somewhat sheltered. There a pure association of Stilbocarpa Lyalhi is visible as far as the eye can reach among the weird and gnarled trunks of Olearia angustifolia and O. Colensoi, which practically make up the shrubby vegetation of this island. Here and there near the shore Veronica elliptica pushes out its green head. Poa Astoni and Crassula moschata grow on the rocks. In a damp place Carex trifida was growing with a patch or two of Asplenium obtusatum and Blechnum durum. Towards the weather side of the island practically no undergrowth is found. Very few young plants are seen. Some young Olearia Colensoi plants, however, caught my attention on account of the great size of the leaves, which by actual measurement were 28.5 cm. long by 14 cm. wide. The above length included the petiole, which measured 2.5 cm.
Here and there among the scrub are some odd plants of Poa foliosa. In open places Tetragonia trigyna is common. In parts of this island, and especially on the south side, the interior of the scrub presented the most extraordinary sight I have ever seen. The trunks of Olearia angustifolia were about 90 cm in diameter at the base, gnarled and bent by the storms in an extraordinary manner. The bark was polished white, and in places was furrowed to a depth of 5 cm., presenting as weird a sight as possible. The ultimate branches turned upwards and closely roofed in the whole plant. Where exposed to the wind, in many cases it was stunted to a height of less than 1 m. On the north side of the island the trunks were fairly straight and the shrubs much higher.
On this side also I noted several specimens of O. Traillii, a plant that has, so far as is at present known, a distribution almost as restricted as any in our flora. The specimens seen by me in their general appearance differed little from O. angustifolia and O. Colensoi, among which they grew, but upon closer examination at once showed the difference in foliage and flower. From the situation in which this species grows, and from its intermediate characteristics, I am inclined to think that O. Traillii may yet prove to be a hybrid between the other two olearias above named. Of course, careful experiments in artificial pollination only can prove whether this theory is correct, and I merely mention the matter for the purpose of drawing attention to the intermediate characteristics of this species.
(1) Rocks and Cliffs.
On this island there is a special cliff association on the southern side. Here the cliffs are sheer down for about 50 m, and the worn and weather-beaten rocks are very noticeable. The Messrs. Hansen Brothers, who have sailed in these waters for many years, inform me that during southerly weather the waves strike these cliffs and splash right over the top. They were under the impression that there was a “blowhole” in the island, but upon examination of the spot with myself it was discovered to be only a sheer-down cliff which in one part slightly overhung.
Some idea of the force of the waves in this place may be gathered from the fact that bits of sawn timber were seen by us right on the top of the
cliff, having been apparently carried there by the sea. Along the top of this cliff—and, indeed, for the greater part of the southern side of the island—practically no serubs grow. The association is a low-growing one, chiefly consisting of Poa Astoni, which covers the ground almost as a sward. Among this grow numerous large, succulent plants of Myosotis albida, much of it in flower, but still with many buds. Round cushions of Gentiana saxosa from 10 cm. to 15 cm. in diameter are common. Apium prostratum is also scattered about, while Selliera radicans and Crassula moschata cling to the rocky surface in parts. Here also I noticed one patch of Anisotome intermedia (?) about 2.5 m. in diameter, and a common sedge, probably Sc [ unclear: ] pus aucklandicus, is also dotted about. In places low bushes of Olearia angustifolia also grow, and in their shelter Blechnum durum and Asplenium lucidum are sparingly found On the brow of the cliff hang screens of Mesembryanthemum australe in full bloom, and Tetragonia trigyna in flower also sprawls over the surface. Here and there Carex trifida grows strongly, with patches of Anisotome intermedia (?). On the level top, where the peat is deeper, there is a considerable patch of Poa foliosa, dotted throughout with isolated plants of Lepidium oleraceum var. acutidentatum. Senecio lautus and Sonchus littoralis were also noted. The above grass is in strong tussock form, about 80 cm. high, with a stem-like base of more or less decayed leaves, and the peat between the tussocks is everywhere full of mutton-bird burrows.
(2) Introduced Plants.
Near the mutton-birders' huts a few introduced grasses and weeds grow, also some Phormium tenax, the latter probably planted by the Maoris on account of its useful qualities.
The Remaining Islands.
The other islands of the group, except one, are quite small, being only about 30 m to 40 m in diameter I did not land on them, but passed close along shore in a boat, thus securing a good view of their general plant formations. The small islands have their summits and more level parts covered with Olearia angustifolia, mixed here and there with O Colensoi.
The cliff-sides are covered with Poa Astoni, with here and there small patches of P foliosa where the exposure is too much for the scrub formation Veronica elliptica clings sparingly to the rocks, and in the sheltered places Stilbocarpa Lyallii can be seen. The largest of these other islands, known as King's Island, or Kaihuka, has, so far as I might judge, much the same covering as Breaksea Island, the associations of which are, I think, fairly typical of the exposed situations throughout the whole group.
The facts of most importance gathered on my visit are those connected with the distribution of the plants in their relation to soil and climate. Olearia angustifolia seems to be par excellence the plant of the exposed seashore on all these islands Stilbocarpa owes its position to the wind-still atmosphere of the interior of the forest and the rich soil of the bird-manured areas. The wind-resisting powers of Poa foliosa are well known, and there can be little doubt that both it and Stilbocarpa confer great benefit on the birds for nesting purposes, and in turn receive assistance from the increased nutrition of the bird-droppings.
Poa foliosa seems to require free access of light, as it is not found under the scrub except on exposed points where the scrub is tolerably open. In these situations occasional tufts of this grass will be found, increasing in number in proportion to the opening among the scrub. This is especially so where the depth of the peat gives special facilities for the bird-burrows. Poa foliosa does not, however, seem to me to make a stable formation, as young plants of both Olearia angustifolia and Veronica elliptica are found amongst it. These plants must gradually take its place by overtopping it, and thus shutting out the light.
As regards Olearia Traillii, I can form no very convincing theory for its being restricted to such a narrow habitat. It is nowhere plentiful, nor are there any very specialized conditions in the association in which it is found. My previous remarks as to the possibility of its being a hybrid constitute the only explanation I can suggest of its presence. Its habit of growth is similar to that of both O. Colensoi and O. angustifolia. Its leaves are intermediate in form between these species. Its flowers are racemed like O. Colensoi, but, unlike the latter, which has practically discoid heads, O. Traillii has short ray-florets, thus placing it in an intermediate position between O. Colensoi and O angustifolia, which has comparatively long ray-florets. As previously mentioned, however, this matter can only be settled by actual experiment.
The number of indigenous species noted on these islands is sixty-nine, belonging to fifty-four genera and twenty-nine families. Appended is a list of them.
List of Indigenous Plants noted.
|Cyatheaceae.||Asplenium flaccidum Forst. f.|
|Dicksonia squarrosa (Forst. f.) Sw.||Blechnum durum (Moore) C. Chr.|
|—— capense (L.) Schlecht.|
|Polypodiaceae.||Histiopteris incisa (Thbg.) J. Sm.|
|Polystichum vestitum (Forst. f.) Presl||Polypodium diversifolium Willd.|
|Asplenium obtusatum Forst. f.|
|—— scleroprium Homb. & Jacq.||Lycopodiaceae.|
|—— lucidum Forst. f.||Lycopodium ramulosum T. Kirk.|
|Dacrydium biforme (Hook.) Pilger.||Leptocarpus simplex A. Rich.|
|Hierochloe redolens (Forst. f) R. Br||Phormium tenax Forst.|
|Poa foliosa Hook f||—— Cookianum Le Jolis.|
|—— Astoni Petrie.|
|Cyperaceae||Thelymitra longifolia Forst.|
|Scirpus aucklandicus (Hook f.) Boeck.||—— uniflora Hook. f.|
|Carpha alpina R. Br||Microtis unifolia (Forst. f) Rchb.|
|Gahnia procera Forst.||Prasophyllum Colensoi Hook. f.|
|Oreobolus pectinatus Hook. f.||Pterostylis Banksii R. Br.|
|Carex lucida Boott.||—— australis Hook. f.|
|—— trifida Cav.||Caladenia bifolia Hook. f.|
|Mesembryanthemum australe Sol.||Pentachondra pumila (Forst. f.) R. Br.|
|Tetragonia trigyna Banks & Sol.||Styphelia acerosa Sol.|
|Dracophyllum longifolium (Forst. f.) R. Br.|
|Cardamine heterophylla (Forst. f.)||Myrsinaceae.|
|O. E. Schulz. var.||Rapanea Urvillei (A. DC.) Mez.|
|Lepidium oleraceum Forst. f. var.|
|acutidentatum T. Kirk.||Gentianaceae.|
|Gentiana saxosa Forst f.|
|Drosera spathulata Labill||Boraginaceae.|
|Myosotis albida (T. Kirk) Cheesem.|
|Crassula moschata Forst. f.||Veronica elliptica Forst. f. var.|
|Pittosporum Colensoi Hook f. var.||Plantago Raoulii Decne.|
|Rubus australis Forst f.||Coprosma lucida Forst. f.|
|—— areolata Cheesm.|
|—— foetidissima Forst.|
|Myrtaceae||Nertera depressa Banks & Sol.|
|Leptospermum scoparium Forst var.|
|Metrosideros lucida (Forst. f.) A. Rich||Goodeniaceae|
|Selliera radicans Cav.|
|Fuchsia excorticata L. f.||Stylidiaceae.|
|Oreostylidium subulatum (Hook. f.) Berggr.|
|Stilbocarpa Lyallii J. B. Armstrong||Compositae.|
|Nothopanax Edgerleyi (Hook. f.) Seem.||Olearia angustii Hook f|
|—— Traillii T Kirk.|
|Umbelliferae||—— Colensoi Hook. f.|
|Apium prostratum Labill||—— arboiescens (Forst. f.) Cockayne and Laing|
|Anisotome intermedia Hook f (?).||Senecio lautus Forst. f|
|—— rotundifolius Hook f.|
|Cornaceae.||Sonchus littoralis (Kirk) Cockayne.|
|Griselinia littoralis Raoul.||Cotula coronopifolia L.|