New Zealand's subantarctic islands lie scattered across the Campbell Plateau, a submerged portion of the New Zealand continental landmass. Before the southwest Pacific Ocean began to form during continental drifting about 80 million years ago, the plateau was connected to Antarctica and formed part of the super-continent of Gondwana. The island groups themselves are primarily volcanic in origin. Campbell Island and the Auckland Islands were glaciated during the quaternary ice ages.
The New Zealand subantarctic islands occupy the cool-temperate zone, they lie between the antarctic and subtropical convergences, have a mean annual temperature above 5 oC, and support a vegetation that includes trees and woody shrubs. True subantarctic islands (e.g., Macquarie Island) lie in the vicinity of the Antarctic convergence, have a mean annual temperature of 1 – 5 oC, and no trees.
Source of information: New Zealand's Subantarctic Islands, Reed Books, 1999.