ABSTRACT
Despite technological advances and an increase in production per unit land-or agricultural intensification-agricultural conversion has been most dramatic during the 20th century. In 1900, cropland covered 40 million hectares worldwide; by 1993, cropland had swelled to 248 Mha. (Brown, 1997b). Though helping to meet food demand, such agricultural expansion has not proved sustainable in many underdeveloped regions of the world and has exacted an environmental toll. Resource degradation linked to rapid deforestation has led to chronic underdevelopment in rural areas (Dasgupta, 1995; Stonich, 1993). Forest elimination can spur soil erosion and sedimentation of waterways, nutrient cycle perturbation, and soil impoverishment (Lai, 1996); these processes, in turn, diminish small farmer capacities to maintain crop yields (Ehui and Hertel, 1992). Tropical deforestation also appears to contribute to global warming (O'Brien, 1995; Tinker et al., 1996) and to the vast majority of species extinction (an estimated 27,000 species-or 90% of the total-annually, according to Myers, 1994). Lastly, since the earth's land is finite, continuing high rates of population growth in developing countries are thought by many to present urgent challenges to the sustainability of systems of food production (Brown, 1997a; Meadows et al., 1992; Pimentel et al., 1994).
