Book excerpt: Views on the dynamics of tropical forests are changing rapidly with the recognition that their environment is variable on the decadal to century scale. Fluctuating climatic conditions partly determine tropical forest structure, species composition and dynamics. Tropical communities are also highly contingent in space and time with respect to site and historical factors. Tropical forests have experienced to some degree this disturbance regime in the past, but climatologists are now predicting increasingly frequent extreme events in the new century. The combination of increasing deforestation and land-use conversion by man plus an increasingly variable environment means a situation that could be very difficult to manage.