Story: Ecoregions

Page 9. The Chatham Islands

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Way out east

The Chatham Islands consist of Chatham Island (the largest), Pitt Island and several smaller islands. They are on the Chatham Rise, an area of continental rocks that once formed part of the New Zealand mainland. The islands have only emerged above sea level in the last 4 million years.

Climate

The climate is cool, wet and windy, and the temperature does not vary greatly from summer to winter. On these exposed islands, plants have to withstand powerful, salt-laden winds. Blowing across hundreds of kilometres of ocean, the winds pick up salt spray that can travel far inland.

Geology

Chatham Island consists of limestone, basaltic hills and dune sand. Together with associated volcanic islands and stacks, it covers about 950 square kilometres. Peat or peat-derived soils cover 60% of the land, forming domes and a deep blanket cover on the southern plateau.

Endemic species

Life forms on the low-lying, isolated Chatham Island group are closely related to mainland species, and to those on the subantarctic islands to the south. Several species of plants and animals are endemic – they are found nowhere else.

Plants

Before human settlement, low broadleaf forest, with a mixture of mainland and endemic trees and shrubs, grew along the coast and on well-drained soils. Drier peat soils had a cover of low scrub, while tall jointed rush (Sporodanthus traversii) and tangle fern (Gleichenia dicarpa) grew in wetter areas.

Many plant types are lacking, notably beeches and conifers. But there are a large number of endemics – mainly island variants of common mainland groups. Perhaps the best known is the blue-flowered, large-leaved herb, the Chatham Island forget-me-not (Myosotidium hortensia).

Fish, birds and insects

The islands are unusual in having an endemic freshwater mudfish, Neochanna rekohua.

Many of the land birds evolved from common mainland birds, including separate species of raven, kākā, four rails, snipe, two ducks, fernbird, bellbird, pigeon, warbler, pipit and robin. All but the last four are extinct. The rails have remarkably well developed beaks – an adaptation to allow them to probe peaty ground. As in all the southern islands there is a variety of seabirds, with many petrels and albatrosses.

The insects, although closely related to those of southern New Zealand, are often flightless and large-bodied.

How to cite this page:

Matt McGlone, 'Ecoregions - The Chatham Islands', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/ecoregions/page-9 (accessed 13 December 2018)

Story by Matt McGlone, published 24 Sep 2007