PREDICTING CHANGES IN THE COMPOSITION OF NEW-ZEALAND INDIGENOUS FORESTS IN RESPONSE TO GLOBAL WARMING - A MODELING APPROACH

A model to predict the effects of global warming on the composition of New Zealand's native forests is described. Relationships between the current distribution of 41 tree species and site temperature, solar ra diation, water balance, lithology, and drainage for 14 500 plots have been analysed using non-parametric regression. Distributions of specie s were then predicted for points on a 5 km grid across New Zealand. A test for residual spatial autocorrelation using a 'proximity' variable , indicated that New Zealand's four Nothofagus species have distributi ons less well correlated with environmental variables than most other species. inclusion of the 'proximity' variable in the regressions also substantially improved predictions of Nothofagus distribution. Predic tions for other species were improved by incorporating a term represen ting interaction with the patchily distributed but strongly dominant N othofagus species. Preliminary results from a cluster analysis of the combined predictions for all species indicate that the model successfu lly reconstructs the existing pattern of New Zealand's indigenous fore sts. Estimation of the effects of global warming on species distributi on was done by introducing a perturbation to represent an overall incr ease in temperature of 2 degrees C. The results indicate that a substa ntial disequilibrium is likely to occur between the current forest pat tern and expected warmer temperatures. Copyright (C) 1996 Elsevier Sci ence Ltd