WATER-ENERGY DYNAMICS, CLIMATE, AND PREDICTION OF WOODY PLANT-SPECIESRICHNESS - AN INTERIM GENERAL-MODEL

Predictable geographic patterns in the distribution of species richnes s, especially the latitudinal gradient, are intriguing because they su ggest that if we knew what the controlling factors were we could predi ct species richness where empirical data is lacking (e.g. tropics). Ba sed on analyses of the macro-scale distribution of woody plant species richness in Southern Africa, one controlling factor appears to be cli mate-based water-energy dynamics. Using the regression models of clima te's relationship to species richness in Southern Africa, I was able t o describe an Interim General Model (IGM) and to predict first-order m acro-scale geographic variations in woody plant species richness for t he continent of Africa, as well as elsewhere in the world-exemplified using South America, the United States and China. In all cases, the ge ographic pattern of variation in species richness is in accord with ge ographic variations in vegetation (visual comparison with vegetation m aps) and net primary productivity. What validation was possible (Afric a and U.S.A.) suggests that the IGM provides 'reasonable' estimates fo r actual woody plant species richness where species richness is in rel ative equilibrium with climate. Areas of over- or under-prediction sup port the contention of earlier workers that edaphic, topographic, hist orical, and dispersal factors need to be considered in a more complete explanation for spatio-temporal variations in species richness. In ad dition to providing a means for systematically estimating woody plant species richness where present-day empirical data is lacking, the Inte rim General Model may prove useful for modelling the effects of climat e change (past/future) on species richness (and, by association, the v egetation).