CLIMATIC GRADIENTS IN WOODY PLANT-SPECIES RICHNESS - TOWARDS AN EXPLANATION-BASED ON AN ANALYSIS OF SOUTHERN AFRICA WOODY FLORA

The distribution of southern Africa's woody flora (N=1372 species) des cribes a west-to-east pattern of increasing species richness, being lo west in arid to semi-arid areas and highest in mesic to humid areas. C limate accounts for 77.8% (R2; P<0.0001) of the variation: species ric hness is greatest where the amount and duration of energy is optimized (not too much, not too little) and moisture maximized, and decreases as the amount or duration of energy moves above or below optimal condi tions, or as moisture decreases. Given the perpetual and necessary rel ationship between climate and plant photosynthesis, climate provides a first-order, albeit partial, explanation for the persistence of patte rn (especially latitudinal and elevational gradients) in the distribut ion of woody plant species richness over space and time.