ABSTRACT

The worldwide evidence that high hills and mountains usually have both more rainfall and more natural forest than do the adjacent lowlands has, historically, led to confusion of cause and effect. Forests contribute to the stability of watersheds by protecting the soil surface from the direct impact of intensive tropical rainstorms. Rainfall is intercepted by the forest canopy, and the foliage temporarily retains a very large area of water films. The desiccation that so often follows the unwise clearing of tropical forests in climates that have a severe dry season is not due to lack of rainfall but to misuse of the land surface. Flood regulation by forests has physical limits that are from time to time overwhelmed by storms of sufficient size and duration. Forests are a major source of foreign exchange earnings for at least 15 developing countries. Watershed management is more difficult in tropical climates that have severe dry seasons because fire becomes a major hazard.