Art VIII.—Notes on Comparatively Recent Changes in the Vegetation of the Taupo District.
[Read before the Wellington Philosophical Society, 28th October, 1914.]
In separate publications, from the time of Bidwill's “Rambles in New Zealand” (published in 1841, although written in 1839) right up to the present time, Taupo has had its share of notice; but, as far as I am aware, no one has written about the changes that have taken place in the appearance of the country at the northern end of Lake Taupo during recent times.
There is a popular delusion abroad that an eruption of red-hot pumice from some centre not specified destroyed most of the vegetation around Taupo, with the exception of some of the isolated patches of forest such as may be seen at Opepe, Oruanui, Tauhara, and many other places. I wish to show in the following notes that the forest at one time covered the whole of the country around the lake, and that the forest has been destroyed by human agency; and, further, to show that there has been no great change in the configuration of the Taupo country for many centuries.
The Taupo country at the present time, with the exception of the patches of bush mentioned above, is covered with what is popularly called scrub, tussock, and fern. The scrub is mainly composed of Leptospermum scoparium, Leptospermum ericoides, Coriaria ruscifolia, Styphelia acerosa, Gaultheria, and Dracophyllum. Of these, the Leptospermum scoparium and Leptospermum ericoides form the main growth, with the Styphelia acerosa and Gaultheria forming thick matted growths among them. The Coriaria ruscifolia grows in among the other scrub in clumps, and is noticeable for miles over the landscape by its dark-green foliage showing above the lighter green of the Leptospermum scoparium and Leptospermum ericoides. The
Dracophyllum has some large areas all to itself, but it is also found in single plants among the other scrub. The tussock is fast disappearing; it is giving place to Leptospermum scoparium and Leptospermum ericoides. The common fern or bracken (Pteris aquilina) grows on the edge of the patches of forest in a thick rank growth, in gullies, and on the hillsides with Leptospermum.
The country has changed very much in appearance during the past few years. Thirty years ago the greater part of the land to the north and east of the Taupo Township was covered with tussock. When fires destroyed the tussock a growth of Leptospermum sprang up in its place and increased so rapidly that now it is hard to realize that where the Leptospermum now blooms the tussock once held undisputed sway.
This change is one of the cycle of changes now going on. If the Leptospermum escapes the ravages of fire for any period above fifteen years, the beginnings of forest growth are seen in the young Coprosma, Pittosporum, and Nothopanax taking advantage of the shelter afforded by the Leptospermum to obtain a start in life. These three families of plants are the forerunners of others, and where the scrub escapes the ravages of fire for a lengthy period nature is hastening to reclothe the country with its ancient forest. I use the term “reclothe” because within the memory of men still living the old forests extended over a much greater area than at present. There is an old Maori now living at Oruanui who remembers the time when the Oruanui Forest extended right on to the edge of the Taupo Lake at Rangatira. The proof of this was to be seen all over that portion of the country up to the last few years The remains of the burnt logs, mostly Podocarpus totara, were collected by the European residents of Taupo, and used as firewood. The last load, as far as I know, was brought in in 1895; but in the more secluded gullies, and where they have escaped the frequent fires, they are still to be seen. Mr. T. McKinley, who has a pastoral lease over a portion of the country mentioned above, has used nothing else for fencing-posts than the old charred Podocarpus totara logs.
A short time before his death, in 1900, an old Taupo Maori named Tahau told me that in the days of his grandfather the clumps of forest now known as Opepe, Motukino, and Tauhara were all connected, and extended over a very large area. It extended out towards the Rangitaiki, the source of the Pueto, the Waikato River, between the present Township of Taupo and the Aratiatia Rapids, and on to the Taupo Lake at Whare-waka. The evidence of this is to be found in the remains of totara logs over all the country mentioned. The old man was between seventy-five and eighty years of age when he died, and if we reckon the boyhood of his grandfather at fifty years prior to his own birth it gives a period of 125 years back from 1900 to the existence of this extensive tract of forest. On the strength of the positive evidence here given we cannot resist the conclusion that in other parts of the Taupo country where the burnt logs are found they must be taken as conclusive evidence of the existence of forest there within very recent times.
The destruction of the forest came about in a very simple way. The staple food of the Taupo Maoris in pre-pakeha days was fern-root, the rhizome of Pteris aquilina. Great quantities of this starchy root was dug up in its proper season every year and stored for use. The best fern-root grew on freshly burnt bush country, and to provide this they were in the habit of burning fresh patches of bush as required. They were accustomed to break down the light scrub and burn it when sufficiently dry. The
fires would destroy the standing timber, and would often spread much farther than intended. In this way the large forests of the Taupo country have been reduced to their present dimensions. These forests can be taken as sufficient to show that no great change has taken place in the surface configuration of Taupo during their time of growth. And as it is usually admitted that the New Zealand forest growth is very slow, it is not too much to place the beginning of the forest at over a thousand years ago.
Up to this point we are on firm ground, but how much further back than the date given above to the beginnings of forest growth it is impossible to determine. The Maori occupation of the country around the lake prior to the time of Ngatoroirangi, Tia, and others of the Arawa people is extremely doubtful; and no other evidence beyond theirs is known to exist.
The forest gives no indication of many generations of large trees. The shallowness of the humus in the forest will not admit of the idea of the decay of generations of the larger forest-trees, and the contours of the country are so sharp that it is quite evident the change from one deposit of pumice to a covering of some kind must have been very rapid. Perhaps the order of change was the same as we have given above—fern, tussock, scrub, forest.
Beneath the surface pumice for several miles around the Township of Taupo there is a deposit of volcanic mud, very much like the mud from the eruption of Tarawera in 1886. This mud can be traced in all the road cuttings leading out from Taupo. On the old Atiamuri Road from Taupo via Oruanui it appears in every cutting, low down in the valleys as well as high up on the hills. It is very noticeable on both sides of the Waikato River near the bridge at Taupo. Beyond Oruanui, on the Mokai Road, it is seen for only a short distance, not quite two miles from Oruanui. On the Rotorua Road, via Wairakei, it can be found for over six miles beyond Wairakei. On the Napier Road it can be traced from the edge of the Taupo Lake to Opepe. The deposit is not found at more than 7 ft. below the surface, except near the edge of the lake, and in many places it is only a few inches. The average depth may be reckoned at 3 ft.
The existence of this stratum of mud at such a depth shows that the surface configuration of the country was almost the same prior to the eruption as it is now.
The source of the mud seems to have been some point near the explosion craters at Rotokawa, the deposit, as far as can be traced, having somewhere about the same thickness at points equally distant from that centre—Taupo, Wairakei, and the hills above the Aratiatia Rapids on the western side having about the same thickness of mud; Oruanui much less; and still farther away from Rotokawa it is not found for more than two miles on the Mokai Road.
There are other questions connected with the age and appearance of the country that the writer does not feel competent to deal with. For instance, the streak of mud we have mentioned appears low down near the present level of the lake, and at least 800 ft. above it. Yet the terraces which mark old lake-levels are formed in the pumice which is on top of the mud. This is very noticeable in the case of the terrace at 120 ft. above the present level. This seems to indicate that when the mud was deposited the surface features were almost the same as at present; that a lake was formed and rose to a considerable height above the present level—how high we cannot a present determine: and that the lake gradually receded, leaving terrace formations, more or less distinct, until it reached its present level.