MODELING PRESENT AND POTENTIAL FUTURE RANGES OF SOME EUROPEAN HIGHER-PLANTS USING CLIMATE RESPONSE SURFACES

It is hypothesized that the principal features of higher plant distrib utions at continental scales are determined by the macroclimate. Biocl imate data have been computed on a 50 km grid across Europe. Along wit h published maps of higher plant distributions based upon the same gri d, these data have been used to derive climate response surfaces that model the relationship between a species' distribution and the present climate. Eight species representative of a variety of phytogeographic patterns have been investigated. The results support the hypothesis t hat the European distributions of all eight species are principally de termined by macroclimate and illustrate the nature of the climatic con straints upon each species. Simulated future distributions in equilibr ium with 2 x CO2 climate scenarios derived from two alternative GCMs s how that all of the species are likely to experience major shifts in t heir potential range if such climatic changes take place. Some species may suffer substantial range and population reductions and others may face the threat of extinction. The rate of the forecast climate chang es is such that few, if any, species may be able to maintain their ran ges in equilibrium with the changing climate. In consequence, the tran sient impacts upon ecosystems will be varied but often may lead to a p eriod of dominance by opportunist, early-successional species. Our sim ulations of potential ranges take no account of such factors as photop eriod or the direct effects of CO2, both of which may substantially al ter the realized future equilibrium.