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Relation to Man and His Agents of Destruction.
There is no evidence of activities of the Maori in the Tararua Mountains. Since the advent of the Pakeha, however, man's influence, direct and indirect, has wrought great changes in the vegetation.
As a first step to destruction of the primitive vegetation roads were made leading into most of the larger valleys. A highway made through the Manawatu Gorge connects the Manawatu River with Hawke's Bay and Wairarapa Plains. Another highway connects Wellington via Rimutaka Saddle to Wairarapa Plains. A little south of this the Wellington–Wairarapa railway crosses the range. The roadmaking has resulted in a most destructive effect on the primitive vegetation. In the author's own experience the native vegetation of the Manawatu Gorge has been reduced enormously within the last ten years. Partly through landslips, consequent upon cutting into hillsides to make room for the road, but largely through repeated cutting and burning of plants along the roadside, introduced plants have been able to obtain a strong root-hold. Among the latter Foeniculum vulgare, Citysus scoparius, Senecio mikanioides, and Vinca major are especially conspicuous, occupying large stretches.
Timber-milling was once in progress everywhere in the foothills, but now is confined mainly to the vicinity of Otaki Forks and Akatarawa River. Dacrydium cupressinum is the much sought-for timber tree. For the most part, especially in the earlier days, the rest of the forest was simply felled and burned and land converted into pastures. Good judgment was not always exercised. Numerous steep hillsides are now to be seen in the Eastern Area either covered with dense growth of Pteridium aquilinum or simply running into large screes.
Farms are not always fenced off from the forest reserves. Even so, as a compensation for the maintenance of the fences, farmers are allowed to run their stock a certain distance into the forest, and a few of them, especially on the eastern side, go as far as to run fires through the regenerating forest adjoining their properties. Because of this very fact that the cattle are allowed access to the
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forest, the dense growths of shrubs and small trees along the margins are soon destroyed, free movement of air is permitted, humidity is appreciably decreased, and the larger trees die slowly but surely one after another through desiccation. Cases of this kind are fairly common.
There are two fairly large water-supply reserves: one, the upper Orongoronga River basin, controlled by the Wellington City Council, and the other, the Tiritea River basin, controlled by the Palmerston North City Council. There are also three large electric power supply dams: one across the Arapeti River and two across the Mangahao River. Practically all of the remainder of the forested area, as well as higher levels, is Crown land controlled by the State Forest Service.
Through the activity of many tramping clubs in the province practically every part of the mountains is accessible along well cut tracks, and their mountain huts provide shelter at frequent intervals.
Through the activity of early white settlers and especially of the Acclimatisation Societies a number of destructive animals of kinds not known in the country before have been introduced into it, some for purposes of sport, others for real or supposed commercial value. The history of introduction is to be found in G. M. Thomson's Naturalisation of Animals and Plants in New Zealand. Cambridge 1922.
Deer (Cervus elaphus) has proved, so far, the most destructive animal on the Tararuas. It is abundant everywhere and especially on and in vicinity of the higher ranges. In many places the ground vegetation is reduced enormously by eating and trampling down. The spongy water-holding property of the soil is also greatly reduced by consolidation. The animal feeds apparently on many herbaceous plants. Of the woody, the following are much favoured: Schefflera digitata, Nothopanax arboreum, N. Colensoi, N. Sinclairii, N. Edgerleyi, Griselinia littoralis, Coprosma australis, C. foetidissima. Apart from feeding on the foliage of these species it also browses on their bark. It is quite common to see many of these trees completely ring-barked by deer from about 80 cm. to 160 cm. above ground. In a few places young Podocarpus ferrugineus suffers in the same manner. The bark of Podocarpus Hallii is often seen stripped, apparently by rubbing with antlers. All these, except perhaps C. foetidissima, usually die. At higher altitudes, when snow is on the ground, young Cordyline indivisa foliage is much favoured. Many meadow species of the subpolar belt are subject to severe grazing. In this respect the lot of Aciphylla Colensoi and Danthonia antarctica is conspicuous, especially where they grow more luxuriantly. The pungent, sword-like leaves of the former do not apparently offer it much protection, while the latter is often on many ridges trampled out of existence and the ground is laid barren. There are a number of places of several hectares in extent, such as are to be seen on top of Mount Quoin and the northern shoulder of Mount Omega, where the wet ground was once covered by luxuriant growth of Danthonia antarctica flavescens nothing but the numerous decaying crowns of it still remained when last seen in 1933. Its place is now occupied by such low-growing bog species as Carpha alpina and Orcobolus pectinatus.
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Wild cattle (Bos taurus) are rather restricted in their distribution on the Tararuas and are practically confined to Otaki Valley, where they are plentiful. Their activity is similar to that of deer.
Goat (Capra aegargus) occurs in numbers in Western Area but is most abundant in the Southern Area. Its destructive habits are well known. Of the individual species attacked, Carmichaelia and Edwardsia seem to suffer most. Many of these plants are to be seen with their crowns hugging the ground, although many years old, because of continuous grazing.
Wild pig (Sus scrofa) is plentiful in the forest, but appears to be especially abundant in the warm temperate belt of the Northern Area. Thus, on the slopes of upper Ruamahanga basin, extensive patches of ground are to be seen thoroughly stirred up and practically devoid of ground vegetation, although sprouting seedlings are fairly numerous.
Opossum (Trichosurus vulpesculus and T. fuliginosus) is plentiful throughout the forest, and is being trapped under licence. Perham (1924) and Cockayne (1928) report very favourably on opossum and consider that it has no important influence on the forest. Recent observations, however, suggest that this animal, like deer, also has selective habits of feeding. Besides, it undoubtedly constitutes potential danger of getting out of control should the market price for its pelts depreciate.
Stoat and weasel (Putorius spp.) are reported by the opossum trappers to be numerous. Since they prey on bird life, they necessarily must have indirect effect on the ravages of insects. Nothing of an exact nature is, however, known in this respect.
Rats (Mus decumanus) and mice (M. musculus) are common, but rabbit (Lepus cuniculatus) and hare (L. europaeus) are absent. Sheep (Ovis sp.) never seem to penetrate into the forest or higher levels.