โ Scribed by J.R. Leathwick; D. Whitehead; M. McLeod
No coin nor oath required. For personal study only.
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 radiation, water balance, lithology, and drainage for 14 500 plots have been analysed using non-parametric regression. Distributions of species 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 distributions 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. Predictions for other species were improved by incorporating a term representing interaction with the patchily distributed but strongly dominant Nothofagus species.
Preliminary results from a cluster analysis of the combined predictions for all species indicate that the model successfully reconstructs the existing pattern of New Zealand's indigenous forests. Estimation of the effects of global warming on species distribution was done by introducing a perturbation to represent an overall increase in temperature of 2ยฐC. The results indicate that a substantial disequilibrium is likely to occur between the current forest pattern and expected warmer temperatures.
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