All New Zealand’s subantarctic islands are parts of the Campbell Plateau, a shallow section of the Zealandia continent extending south and east of New Zealand.
The Auckland, Campbell and Antipodes islands are primarily of recent volcanic origin. The first two are eroded volcanic domes created 10–15 million years ago. The western sides of all three groups have been eroded significantly, creating steep cliffs, while on the eastern sides lava flows and glaciers from the Pleistocene era (about 2 million years ago) have formed U-shaped valleys, fiords and harbours. The Antipodes volcano is the youngest and least eroded.
The Snares and Bounty islands are outcrops of granite similar to the southern part of Stewart Island.
Apart from the Bounty Islands, which are covered in guano and support almost no plant life, the subantarctic islands have a layer of peat, the remains of plants, which in flat areas is up to 5 metres thick. This acidic soil restricts the growth of many introduced plants.
The geographic isolation of the islands, their peaty soil and the windy and sunless climate have produced a unique plant life with many species endemic to the region. Some plants are New Zealand species, or related to them, but there are also unique species. On the Auckland Islands alone there are 34 rare species and six endemic taxa (groups of taxonomically related species). Campbell Island has five and the Antipodes Islands four. The first great botanist of the region, Joseph Hooker, believed that the flowering plants of the islands were ‘more remarkable for their beauty and novelty than the flora of any other country’.1
Hooker was specifically referring to megaherbs, unique species of alpine flowers which have developed large leaves to cope with the absence of sun, and which have brightly coloured blooms to attract insects. They include the red-flowering daisies Pleurophyllum criniferum, P. hookeri and P. speciosum, Stilbocarpa polaris with its huge rhubarb-like leaves, the spectacular yellow flowers of Bulbinella rossii and the more delicate blue forget-me-nots, Myosotis Antarctica and M. capitata. However, the megaherbs have been seriously damaged by introduced animals such as sheep and goats, and only on Adams and Disappointment islands in the Auckland group do they flower in their full glory.
Tussling with tussock
The Poa tussock on the Antipodes Islands grows up to 1.5 metres high above massive trunks of dead and rotting leaves. The fastest way to make progress through the tussock is to step from one top to the next, but this is not easy. Naturalist Herbert Guthrie-Smith described how ‘[v]ainly attempting to keep his balance the walker might at one stride be semaphoring high and tall, desperately gesticulating, the next his shoulders only might be visible above the treacherous mat of grass.’2
On the upper slopes of the Auckland and Campbell islands tussocks are widespread, while the Antipodes Islands are dominated by a pale tussock (Poa litorosa) and deep green ferns (Polystichum vestitum).
Trees and shrubs
Forest trees are found only at lower altitudes on the Snares and Auckland islands. Further north and warmer, the Snares Islands are home to a forest predominantly of Olearia lyallii (a relative of the leatherwood found below the bush line in New Zealand). The lower slopes of the Auckland Islands are a dwarf forest of southern rātā (Metrosideros umbellata), which flowers spectacularly in summer, with the occasional tree fuchsia and the world’s southernmost tree fern (Cyathea smithii).
Campbell Island has a thicket of tall shrubs, especially Dracophyllum and a few Coprosma. It also has one lonely tree, a 6-metre spruce planted in the early 20th century to mark the 1901 visit of Governor Lord Ranfurly.