Evolution and distribution of the New Zealand flora, as affected by quaternary climates

Summary The present distribution and ecology of New Zealand plants is discussed from a historical viewpoint.It is suggested that during the Miocene a southern extension of the New Zealand archipelago supported a cool temperste flora, which gave rise to the present mountain flora after the onset of orogeny and climatic cooling in the Pliocene.As there was scarcely any simultaneous development of a distinctive flora adapted to the dry conditions which prevail to the east of the mountain axis, Cockayne§ opinion that extremely arid Pleistocene climates evoked certain characteristic life forms—notably the divaricating juvenile form of some trees—is considered to be substantially incorrect. That these life forms are adapted to still–existing conditions seems more probable. The broader features of present distribution are explllined in terms of Pleistocene glaciation and subsequent climatic amelioration.From the evidence of endemism and discontinuous distribution, it is concluded that Otago and Southland,Nelson and Marlborough, Auckland,the subantarctic regions and the Chatham Islands are areas where much of the present flora survived during the glaciation,whereas the middle portion of the South Island and the south of the North Island were characterised by extinction.Adjustment of the vegetation to post Pleistocene conditions is still incomplete, and complicated by the effect of continuing climatic fluctuations.