Forest Vines to Snow Tussocks: The Story of New Zealand Plants
These islands lie about 820 km east of Banks Peninsula at 44°S. The main island is about 45 km north to south with a narrow waist 8 km across, widening to about 50 km in the north and to about 25 km in the south. The island is generally low lying with the highest point in the south only 284 m. About one quarter of the island's area is taken up by the Te Whanga lagoon and there are a number of other smaller lakes. Pitt Island, 16 km by 8 km, a little to the south, is the only other island of any size.
The Chatham Islands are a little greater in area than the Aucklands and lie in milder latitudes, so they have a larger vascular flora of about 320 species with a higher proportion of woody plants. At least 29 of the species and 8 susbspecific taxa are endemic and the great majority of the remainder are shared with New Zealand.
Rainfall on the main island is moderate, ranging from a minimum of 600 mm in the lowlands to probably over 1200 mm on the southern table land. Cool south-west winds predominate, atmospheric humidity is high, skies are often cloudy and temperatures are relatively cool for the latitude. Frosts, however, are rare and a few droughts exceeding 15 days can be expected each year. It is not a climate that one would expect to lead to the extensive development of peat, but in fact 60 per cent of the land surface is covered by peat and peat soils. Most of the peat is in raised bogs maintained by rainwater and hence is of low fertility. Wright,168 who surveyed the soils of Chatham Island, suggests that a high level of salt deposition from strong winds may inhibit decay of plant litter and so encourage peat formation on the many flat or gently sloping sites.
Again there are some difficulties in reconstructing the original vegetation as a long period of Maori occupation was followed by European settlers with their attendant sheep and cattle. Early botanical accounts, especially that of Cockayne169 early this century, are helpful in determining the nature of the original vegetation cover. At these earlier times, although there were still extensive forests, a number of the hillslopes and ridges at lower elevations and some ridges at higher elevations were occupied by a low plant cover dominated by bracken fern. As on the mainland this community was probably induced by Maori fire.page 213