**Author details**

The intensity of human impact on tropical environments is documented in the large areas that have been subjected to deforestation. The impact has affected the geomorphic processresponse system, the nutrient cycles, and biodiversity. Recent studies have shown that there is no reversal in the overall trend of tropical deforestation, though the rates of deforestation vary strongly from one decade to another and from one country to another, depending also on the methods used to assess deforestation [2, 28, 79, 39]. Estimates of the world-wide con‐ tribution of deforestation in the tropics to carbon emissions indicate a total emission of 810

 metric tonnes/year (period 2000 to 2005) excluding carbon emissions from logging, peat‐ lands drainage and burning, and forest recovery [39]. However, the contribution of carbon emissions from tropical deforestation to global climatic change remains obscure as the turn‐ over rates and recovery rates are related to various factors and the interaction between these factors is not completely understood [35, 38]. This applies also to the effects of global climat‐ ic change on the geomorphic process-response system as changes in magnitude and fre‐ quency of geomorphic processes depend also on all other environmental changes. Predictions on future climatic development trends in the tropics suggest an increase in summer monsoon and a decrease in summer rainfalls in Central America and Mexico and an increase in the number of cyclones, tropical storms and hurricanes [44]. However, human interference and climatic change often act simultaneously. This complicates predictions of crucial thresholds and the establishment of relationships between landsliding and large soil erosion events and the spatial distribution and the seasonal and annual variability of rain‐ fall. The temporal clustering of landslide events in some regions, on the other hand, appears to indicate some associations. In Kenya landsliding was closely associated with the occur‐ rence of El Niňo circulation [52]. In southern America, on the other hand, the temporal pat‐ tern of landslide events appears to coincide with the ENSO climatic cycle. However, hillslope processes are characterized by an intrinsic complexity. Many factors appear to be capable of causing changes in both frequency and magnitude on different spatial and tem‐

Studies on deforestation rates in several countries of humid tropical Africa have shown that the rate of forest destruction is not only a result of the growth in population but depends also on macro-economic changes. Apart from dependence on international market prices, the extent of the agricultural area appears to depend directly and indirectly on factors such as public investment, monetary policy and exchange-rate policy, urban income levels, fertil‐ izer subsidies, and rural-to-urban and urban-to-rural migration [50, 64, 65]. With respect to

the issue of sustainable development, socioeconomic factors must also be considered.

A significant statistical relationship has been determined between the decline of the cocoa and coffee prices and subsiding governmental input, which has forced farmers in Cameroon to expand their food and crop cultivation into forested areas [51]. International prices and demands on agricultural resources, on the other hand, often result in an expansion of agri‐ cultural areas at the expense of rain forests. An example is the expansion of agricultural areas for soybean production and the increase in cultivated pastures in Brazil, which result‐ ed from the growing importance of cattle ranching. The expansion of soybean cultivation re‐

\*106

20 Environmental Change and Sustainability

poral scales.
