and ecosystem dynamics. Land or forest degradation occurs when these changes are of sufficient magnitude to have a long-term negative effect on productive potential. Forest transformation occurs when the original forest is eliminated and replaced with permanent agriculture, plantations, pasturelands, and urban or industrial developments.

Estimates of the original and current humid tropic forests are difficult to present, especially concerning forest type. The original extent of tropical rain forests (apparently excluding tropical moist deciduous forests) has been estimated to total 1.5 billion ha, with 600 million ha having been cleared and converted over the past several centuries (Ehrlich and Wilson, 1991; Food and Agriculture Organization and United Nations Environment Program, 1981). The current extent of tropical rain forests and tropical moist deciduous forests has been estimated to be 1.5 billion ha, with 1 billion ha considered to be intact or primary forests in which human activity has had little impact (World Bank, 1991). Apparently Africa has lost the greatest proportion of its original tropical moist forests (about 52 percent), followed by Asia (42 percent) and Latin America (37 percent) (Lean et al., 1990). Figure 1-1 illustrates the original and present extent of tropical rain forests historically and at present.

During the past two decades, the rate of conversion in the humid tropics has accelerated (Table 1-4), although comparisons of data collected over several decades are unreliable due to differences in data gathering methodologies and definitions of area, type of forest, and deforestation. However, the accuracy of more recent information on the rate, extent, and nature of forest conversion is improving.

Forest resources appraisals are part of the mandate of the FAO. The last worldwide assessment was carried out with 1980 as the reference year (Lanly, 1982). An assessment with 1990 as the reference year was launched in 1989 to provide reliable and globally consistent information on tropical forest cover and trends of deforestation and forest degradation. Deforestation refers to change of land use or depletion of crown cover to less than 10 percent. Forest degradation is defined as change within the forest that negatively affects the stand or site and, in particular, lowers its regenerative capacity.

The first interim report of the Forest Resources Assessment 1990 Project (1990) contained preliminary area estimates at the regional level for 62 countries lying mostly in the humid tropic zone. Comparison with the 1980 assessment is possible for 52 countries covered by both assessments; definitions of forest and deforestation are basically the same. The estimated deforestation rate for the period 1976