1 Introduction

The Latin American tropics and subtropics contain many unique ecosystems of high biological diversity, many endemic species, and a great potential in terms of renewable natural resources. The ecosystems have evolved under climatic regimes of relatively low variability, characterized by high temperatures and precipitation, resulting in very complex and intricate ecological interrelationships. On the other hand, the ecosystems exhibit a high degree of fragility in face of human perturbations, particularly those associated with the indiscriminate application of modern technologies originating in the industrialized countries and generated under quite different climates and social settings.

However, indigenous pre-Hispanic cultures and civilizations had reached a rather sophisticated level of technology in the management of complex ecosystems, which proved to be sustainable over long spans of time. Different civilizations such as the Maya, the Inca, and the hydraulic cultures of Brazil, Bolivia, Colombia, Ecuador, and Mexico, maintained sustainable agricultural production for centuries, developing original and efficient solutions for managing the environmental resources without destroying the ecological base of production, at relatively high population densities and often including metropolises of considerable size (GallopÍn, 1985; Gligo and Morello, 1980; Vitale, 1983).

The fragility of the Latin American tropical ecosystems, therefore, must be considered in relation to the technology utilized, and not necessarily as an intrinsic attribute precluding any kind of human intervention.

It is clear, however, as will be discussed later, that the current trends in the region are characterized by very high and accelerated rates of ecological deterioration, expressed as deforestation, desertification, soil erosion and depletion, agricultural, industrial, and domestic pollution, accumulation of wastes, and increased vulnerability to catastrophic landslides, droughts, and floods (CEPAL/PNUMA, 1983a; Damascos et al., 1989; Doureojeanni, 1982; Sancholuz et al., 1989; Sunkel and Gligo, 1980). A large proportion of those changes occur in the tropical and subtropical areas of the region, where the advance of the agricultural frontier is most dynamic.

The problem lies not in the transformation or alteration of the natural ecosystems (transformations that in principle could be positive), but in the actual modality and results of these transformations, implying an accelerated degradation of the ecological basis of production, a veritable impoverishment and destruction of the region's renewable natural resources and vital ecological processes. It should be emphasized that many alterations, such as desertification and soil erosion, are irreversible in practical terms.

The destruction of the Latin American tropical ecosystems, and particularly of the tropical forests, is cause for serious concern. From the regional and local viewpoints, the destruction of forests, besides representing a waste of resources for development, has serious ecological impacts, generating micro- and mesoclimatic changes, through variations in the albedo and residence time of rainwater, increases in surface runoff, reductions in evapotranspiration, increases in maximum temperatures and daily thermal amplitudes, and reductions in precipitation (Salati et al., 1989), as well as soil erosion, floods, and other effects. From the global viewpoint, tropical deforestation is a significant contributor to the greenhouse effect, and might possibly affect the regulation of the planetary atmospheric circulation; tropical deforestation is also considered one of the major current causes of species extinction.

In the face of this situation, it is worth investigating the potential for a sustainable management of the major tropical ecosystems in

Latin America. While a number of studies are available around the world, addressing the issue of sustainability at the micro-level and examining alternative technical solutions for the sustainable use of natural resources by a particular human community, or for a given specific ecosystem, studies at the macro-level (regional or global) are very scarce. This paper presents the results of an investigation of sustainability for the whole of tropical Latin America, centred on an ecologically and technically feasible prospective scenario. This scenario is defined as an alternative to the ecologically degrading trajectory being followed in the region.