Environment – The Chatham Islands

The Chatham Islands Environment

The Chatham Islands are home to a number of ecologically significant conservation reserves and habitats with threatened and uncommon plant and bird life, including 18 bird species unique to these Islands. Of the 460 indigenous flora on the Chathams 41 species including one genus the iconic Chatham Island forget-me-not (Myosotidium hortensia) are found nowhere else in the world. The Chatham Islands are also home to 30% of New Zealand’s threatened species and it has the highest level of endemism in the New Zealand biogeographic region - 47 plants and fungi, 10 seaweeds, 16 bird, one lizard and over 50 invertebrates are unique to the islands. A number of the Island’s birds are on world birding lists, with viewing highly sought after by many in the international birding community. The unique flora is also attracting increasing numbers of visitors to see these special plants in their wild habitats.

Dr Peter J de Lange, Associate Professor, Unitec Auckland

Chatham Islands Geology

The Chatham Islands are remarkable because of their location on the Pacific Plate, some 800 kilometres east of the active plate boundary with the Australian Plate. Because of this distance from all the action they are the most stable part of New Zealand in terms of earthquake and volcanic hazards.

The Chatham Islands may also be thought of as an eastern-most outpost of land within the largely submerged 7^th continent of Zealandia.

There is ample evidence of a long protracted submarine history for much of the past 70 million years. Land only became established less than six million years ago.

In many ways, the geology of the Chathams is like an uplifted ‘window’ on the geology of the Chatham Rise, dominated by submarine volcanoes and fossil-rich marine sediments such as limestones. The flat-lying landscape is largely the product of marine ‘planation’ as it was pushed up out of the sea and yet the oldest rock formations reveal a long whakapapa that predates Zealandia, back to Gondwana.

Read more about the geology of the Chatham islands here: >>>>>>

Chatham Island Plants and their habitats

The Chatham Islands has a special and distinctive flora, despite retaining strong affinities with mainland New Zealand. Of the 465 indigenous, vascular plant taxa recorded, 40 are found only on these Islands (endemic) and two of these are found nowhere else in the world. They are the Chatham Islands forget-me-not, also known locally as Chatham Islands lily, and the Chatham Islands sow thistle.
The natural habitat for both are the coastal sand dunes. The horticultural potential of the Chatham Islands forget-me-not was recognised over 150 years ago; it is world renowned for its size, beauty and ease of cultivation.

While many of the other endemics have diverged from relatives scattered throughout New Zealand, most of the other vascular plants show strong connections to northern, rather than southern parts of New Zealand.

Trees and shrubs make up only 8% of the Chatham Islands vascular flora compared with 24% in New Zealand and many of the characteristic forest trees of New Zealand, such as the podocarps (rimu, totara, etc.) and southern beeches are absent from the Islands.

Only about half the plant families found in New Zealand are represented on the Chathams, with ferns and their allies making up nearly a quarter of the flora. Nearly 60% have fruit or seeds suited to long-distance dispersal by seabirds, waterfowl, wind or water.

The varied topography of the Chatham Islands, from the coastal dunes, backswamps and flatlands, to the gently rolling and steeper hillslopes and cliff-faced plateaus provides a range of different habitats for Chatham Island plants. Sand dune vegetation is extensive, with marram grass (introduced in the 1890s to stabilise the dunes) dominating, but indigenous shrubs and herbs are common. Good examples of the sand dune communities occur on Long Beach near Henga, and on Kaingaroa and Waitangi West beaches.

Formerly, coastal broad-leaf forests occurred on the sand dunes and inland for up to a kilometre or more on the better drained soils around most of the Islands. Today, regenerating forest can be seen at the Henga Scenic Reserve, Admiral Gardens, Nikau Bush, Ocean Mail and Point Munning on Chatham Island and in the Pitt Island reserves.

Inland, on the deeper and wetter peaty soils, tarahinau forest dominates, with a mixture of broad-leaf species, many tree ferns, smaller ferns, and shrubs on the drier sites, with open heathlands and swampland interspersed in the wetter hollows. Best seen on the southern cliffs and near Awatotara.

Heathlands and wetlands occur where the watertable is near the surface, the vegetation dominated by a mixture of shrubs, flax, ferns, sedges and rushes. The Ocean Mail boardwalk and the Aster walk provide good examples of these communities.

Distinctive rock types: The limestone outcrops at Blind Jims, the schist at Point Munning and the trachyte of Mount Hakepa on Pitt Island all carry a range of interesting plants that are well worth checking out.