CLIMATIC RELATIONSHIPS OF SOME NEW-ZEALAND FOREST TREE SPECIES

A dataset of some 10 000 plots was used to describe the climatic relat ionships of 33 widespread New Zealand tree species. Estimates of mean annual temperature, temperature seasonality, mean annual solar radiati on, and moisture balance were derived from mathematical surfaces fitte d to climate station data. plots were also categorized into five litho logical classes and three drainage classes. Generalized additive model s were used to examine species/environment relationships. Mean annual temperature and mean annual solar radiation are most strongly correlat ed with current tree distributions, followed by moisture balance, temp erature seasonality, lithology, and drainage. Most broad-leaved tree s pecies other than Nothofagus spp. reach their greatest levels of occur rence in warm, moist environments with high solar radiation. In contra st, Nothofagus spp. generally reach their greatest levels of occurrenc e in cooler and/or lower insolation environments, and all have lower l evels of occurrence on rhyolitic substrates which have resulted from l arge-scale geomorphic disturbance, mostly over the past few thousand y ears. Although coniferous species have widely differing climatic optim a, many are biased towards lithological classes characterized either b y large-scale geomorphic disturbance or harsh edaphic conditions. The relevance of these results to particular synecological questions is br iefly discussed. Continuing adjustments in the range of slow-dispersin g Nothofagus spp. are strongly suggested, and the climatic suitability of extensive rhyolitic basins in the central North Island, from which these species are largely absent, is confirmed.