Plant biogeography and the late Cenozoic history of New Zealand

Abstract

Patterns of regional endemism, vicariance, and disjunction in New Zealand higher plants are reviewed. These are discussed in relation to the post-Oligocene history of the geology, climate, and vegetation. Previous explanations for such distribution patterns have ccntred on the disruptive effects of ice and severe climates during the Last Glaciation, and subsequent migration of plants from glacial refugia during the postglacial. It is concluded that these explanations arc largely inadequate. It is suggested that many endemic, vicariant, and disjunct plant distributions are related to the large-scale modification of the New Zealand land mass which has occurred as a result of active tectonism since the Oligocene. The more stable regions of New Zealand (in particular Northland, northwest Nelson, and Otago) have retained diverse floras partly as a result of retention of older elements of the flora which more radically altered areas (southern North Island, central South Island) have tended to lose. The rapidly rising Southern Alps may have acted as a centre of speciation because of its provision of novel alpine and subalpine environments. Glaciations have affected distribution patterns mainly through permitting the wide spread of glacial environment specialists.