Page 10 – The southern islands
To the south of the mainland lie scattered groups of small islands (Bounty, Snares, Antipodes, Campbell, Auckland and Macquarie). These are often called the ‘subantarctics’.
Macquarie is an Australian territory, but it is ecologically closer to New Zealand’s subantarctic islands. The southern islands all lie between two oceanic convergences:
- south of the subtropical convergence, where the warm, salty waters of the northern ocean meet the cooler, fresher waters of the south
- north of the Antarctic convergence, where the cold southern ocean begins.
The climate is windy and cloudy, with persistent light rain and little sunshine. Although it is humid and cool, temperatures do not vary greatly from summer to winter.
Soils and vegetation
Deep, dry peat soils cover almost the entire landscape. They support forest, scrub, grassland or herbfields. In poorly drained valleys and on plateaus, deep raised bogs have formed, with tussock or cushion bog vegetation.
The nutrient-rich waters hold an abundance of krill, squid and fish, and marine mammals and birds that feed on them. These small patches of land are home to some of New Zealand’s most biologically interesting species, such as the New Zealand sea lion (Phocarctos hookeri).
The Bounty Islands are a small group of granite islets totalling just over one square kilometre. There is no soil and few plants, but a number of endemic marine birds and insects.
The Snares are the remnants of granite outcrops, covered in deep dry peat, scrub and grassland.
Macquarie Island, the furthest south of the group, is an uplifted sliver of ocean-floor basalt. Despite its southern position it was never glaciated. Clothed largely in tussock grassland, herbfield and tundra, it has no woody species.
The remaining three island groups are all mountainous remnants of basalt volcano domes. These have been eroded into sheer sea cliffs on their exposed western sides.
Antipodes Island is dominated by grassland fern, with herbfield higher up, and two species of coprosma (the only woody plants) in sheltered sites.
The Auckland Islands and Campbell Island are mountainous, extensively sculpted by glaciers.
Auckland Island has a tall rātā forest (also home to the southernmost tree fern) on the sheltered side. Higher up, this gives way to scrub, tussock grassland, herbfield and tundra.
Campbell Island is at the southern limit of tree growth at this latitude of the southern hemisphere. The lowlands are dominated by dwarf forests of dracophyllum.
The larger islands have spectacular tussock herbfields on exposed westerly cliffs.
Plant species have mostly been dispersed from the New Zealand mainland, and many are common to most islands. However, there are about 60 unique species of shrubs and herbs, including the spectacular large-leaved forms. Their leaves, some up to 50 centimetres across, appear to be specially adapted to harvesting energy from the cool, cloudy, ocean climate.
The islands are home to many sea mammals including southern sea elephants, Hooker’s sea lion and three fur seals.
Marine birds are abundant, with numerous petrel, prion, albatross and penguin species. Many have developed into different species. Most island groups have their own species of shag, rail, duck and parakeet. There are also snipe, tomtits, fernbirds, and pipits that are found nowhere else.
Loss of flight
Many birds and insects are unable to fly, or are poor flyers. For insects, this may be because of the high winds. For birds, it is probably because there were no land predators.
The southern parakeets seem to have become partly carnivorous, eating eggs and scavenging dead birds, or even hunting small petrels.