SENSITIVITY ANALYSIS OF VEGETATION DIVERSITY TO ENVIRONMENTAL-CHANGE

A model is presented for predicting the global distribution of family diversity in natural terrestrial vegetation. The model assumes that three primary mechanisms determine diversity: the capacity to survive the absolute minimum temperature of a site, the ability to complete the life cycle in a given length and warmth of the growing season, and the capacity to expand leaves in a defined regime of precipitation and vegetation transpiration. The model is tested for present-day vegetation and shows good agreement with observations from local floras. The sensitivity of family diversity to global environmental change has been tested by applying different combinations of greenhouse warming scenarios (+ 3-degrees-C, +/- 10% precipitation, +/- 2 x CO2 concentration) to all vegetation types. About 50% of the floristic regions of the world exhibit a reduced diversity with a 3-degrees-C increase in temperature. Diversity is further reduced by a 10% decrease in precipitation. A doubling of the CO2 concentration may be equivalent to an increase in precipitation of 10 - 20% through its capacity to reduce transpiration.