RESPONSES OF TROPICAL TREES TO RAINFALL SEASONALITY AND ITS LONG-TERMCHANGES

Seasonality and physiognomy of tropical forests are mainly determined by the amount of annual rainfall and its seasonal distribution. Climat ic change scenarios predict that global warming will result in reduced annual rainfall and longer dry seasons for some, but not all, tropica l rainforests. Tropical trees can reduce the impact of seasonal drough t by adaptive mechanisms such as leaf shedding or stem succulence and by utilization of soil water reserves, which enable the maintenance of an evergreen canopy during periods of low rainfall. Correlations betw een climate and responses of tropical trees are therefore poor and the responses of tropical rainforests to climatic changes are hard to pre dict. Predicted climate change is unlikely to affect the physiognomy o f rainforests with high annual rainfall and low seasonality. Seasonal evergreen forests which depend on the use of soil water reserves will be replaced by more drought-tolerant semideciduous forests, once rainf all becomes insufficient to replenish soil water reserves regularly. A s the limits of drought tolerance of tropical rainforests are not know n, rate and extent of future changes cannot be predicted.