The Effects of European Settlement^129,130

This book is largely concerned with the native flora of New Zealand which has been evolving here for many millions of years. Changes brought about by Europeans, in particular the establishment of introduced plants or 'adventives', has occupied just a moment of geological time. It is appropriate to consider these recent changes in this chapter as they tend to involve lowland open habitats.

A major aim of the European settlers was to establish farms, particularly sheep farms for the production of wool and meat. Naturally the grasslands of the eastern South Island and southern North Island were exploited first, since there was no forest to be cleared and less possibility of conflict with the Maori, whose numbers were lower in the South Island.

The initial development of sheep runs on the natural grasslands took place from the 1840s to the 1860s. At first the sheep were grazed on the native grasses, but as these were mostly coarse and not very palatable a practice developed of periodically setting fire to the grassland to induce soft new growth from the tussocks. This resulted in loss of humus and reduced the fertility of the soil, so eventually the degraded short tussock grasslands of the Canterbury Plains and parts of Otago page 161

Figure 89 View of the Olivine Range showing a contact between ultramafic rock (left) and schist (right). On the schist there is the normal forest to alpine vegetation sequence, on the ultramafic rock this is absent and there is a sparse cover of shrubs and herbs without a clear altitudinal zonation.
Photo: P. F. Newsome.

were replaced with European pasture grasses or grain crops.

In the higher country burning continued, and this, combined with overgrazing and the depredations of other introduced animals, particularly the rabbit, led to degeneration of the native vegetation. In places, tall tussock grassland changed to short tussock grassland, and elsewhere short tussock grassland became virtual desert. The situation has improved somewhat in recent years with the cessation of burning and the control of rabbits.

After the end of the New Zealand Wars in the North Island in the 1870s, extensive forest clearance began. In the north, the main purpose was to obtain valuable construction timber from the forests containing kauri. Elsewhere, obtaining timber was secondary to land clearance for sheep or dairy farming, and the forests were often destroyed by fire.

The fernlands and shrublands of the eastern North Island were also cleared for farming, but this was not successful on the volcanic plateau until the cobalt deficiency of the soil was corrected. In this region extensive plantations of exotic pines have been and are still being established.

As the higher mountain areas are unsuitable for human settlement, it might be expected that the alpine vegetation there would have been page 162little altered since the arrival of human beings. It has been less altered, certainly, but introduced wild animals, notably deer and in places goats and thar, have reduced palatable species and interfered with natural regeneration. As with the rabbits at lower elevations, some success has been achieved in controlling the numbers of these animals, particularly since the advent of deer hunting by helicopter. In places in the mountains some alpine plants which had become rare are now re-establishing.

Deer have also been a problem in the forests, as has the introduced Australian opossum, which may entirely defoliate some palatable species such as northern rata (Metrosideros robusta) and five-finger (Pseudopanax arboreus).

Since European settlement a considerable number of plants from other countries, most notably Europe, have been deliberately or accidentally introduced. Some of these have established themselves in the wild, mainly in the settled lowlands, and are known as the adventive flora. Many of the adventives are herbaceous, often annual weeds of disturbed and waste places, and are not individually conspicuous. Some cover more extènsive areas and may form pure associations. Examples are gorse, particularly about Wellington; blackberry and broom in many areas; lupin on sand dunes; california thistle and ragwort in cultivated areas; nassella tussock in North Canterbury; sweet briar and sheep's sorrel on the drier eastern South Island; thyme in Central Otago; and in the northern North Island water hyacinth, which is presenting a problem by blocking streams and lakes. The more cold-tolerant water weeds Elodea and Lagarosiphon appear to be spreading through both islands.

The adventives seemed so aggressive and successful that some early observers feared that the native flora was endangered. Armstrong¹³¹ wrote: 'The rapidity with which foreign plants become naturalised in New Zealand is indeed a most surprising and extraordinary circumstance, as it must be quite evident to every observer that the introduction of these European plants will certainly result in the extermination of the indigenous flora, and that at no distant period of time.' Cockayne¹³² disagreed with this view. He considered that few adventives were successful where native vegetation was well established. This is still generally the case. Examples of the few exceptions are Scottish heather, which is well established in Tongariro National Park, and Pinus contorta, which is an increasing problem in the same area.