The international political economy of tropical rainforests related to their perceived role in global climatic change has to be set against real national and local political economies. These political economies involve socially driven biophysical responses with economic and social costs whose magnitude and distribution need to be known if policy formulation for improvement of living conditions is to succeed. Spatial linkages between changes and social costs, such as the downstream impacts of logging, need to be established, but before that can be done it is necessary to distinguish the effects of natural processes from those induced by people. In Malaysia logging or ground clearance increases river sediment yields by two to fifty times. Individual estimates may be unreliable indicators of the overall effects of change. However, the modifications to rivers as a result of raised sediment loads are increasing year by year. Site-based studies of the effects of both logging and shifting cultivation help to improve the data base for policy making and also indicate the efficiency of reduced impact logging and agroforestry techniques.