Introduction

The humid tropics comprise about 31 per cent of all tropical biomes, cover 11 per cent of the earth's total surface, occupy about 1.5 billion ha of land area, and are home to about 2 billion people (WRI 199091). Of the 1.5 billion ha of the humid tropics, 45 per cent lie in the Americas, 30 per cent in Africa, and 25 per cent in Asia and Oceania. Within the generic term "tropical rain forest" (TRF), there are three principal types of forest vegetation including: lowland rain forest (80 per cent of the humid tropical vegetation), premontane forest (10 per cent), and lower montane and montane forests (10 per cent). The TRF ecosystems are characterized by constantly high temperatures and relative humidity, high annual precipitation, highly weathered and leached soils of low chemical fertility, and high total biomass. High total biomass production, despite low soil fertility, is due to the effect of high temperatures and relative humidity, abundant rainfall, and low moisture deficit. The natural vegetation of the TRF is characterized by a high degree of biodiversity. The TRF ecosystem has global importance in terms of soil and climatic interactions and its impact on several processes. For example, local and global climatic patterns are influenced by the interaction of the TRF with the atmosphere (Salati et al. 1983; Myers 1989; Houghton 1990). An important aspect with global influences involves the impact of the TRF on biogeophysical cycles, e.g. C, N, S, and H2O. Conversion of the TRF to other land use disrupts these cycles, which are critical in regulating several global processes; e.g. emission of radiatively active gases into the atmosphere, change in the total water vapour present in the atmosphere. It is because of these local, regional, and global interactions that the TRF and its conversion are a major concern.