each year. However, the growth in yield rates for cereal crops in Asia is increasing more slowly than demand (Harrington, 1991). Fallow periods that formerly allowed for the accumulation of nutrients and the suppression of pests have essentially been removed from the crop rotation sequence, their role being assumed by applications of purchased chemical inputs. Furthermore, pressures from pests and diseases are increasing as the area devoted to the cultivation of new varieties increases in size (Fearnside, 1987a).

In many countries, lowland areas that are relied on for producing staple and cash crops are in danger of becoming unfit for crop production as a result of improper management. The inappropriate use of high-productivity technologies is being implicated in various forms of natural resource degradation, including nutrient loading from fertilizers, water contamination from insecticides and herbicides, and waterlogging and salinization of land (Harrington, 1991). Loss of lowland cropland could seriously impair the capacity of countries in the humid tropics to meet future food demands.

The pressure to meet the subsistence needs of populations is causing governments to convert additional lowland as well as upland areas. In Indonesia for example, as transmigration programs continue, previously unmodified wetland ecosystems are being considered for cultivation of irrigated, monoculture rice or for mixtures of coconut plantations with secondary crops, which are grown to meet local needs rather than for cash or market (Kartasubrata, Part Two, this volume). In some areas, the high risk of malaria, schistosomiasis, and other diseases remains a significant barrier to the use of lowland areas. At present, these health concerns are greatest in the humid tropics of Africa and Asia.

To the extent that productivity in lowland areas declines and forested upland areas are environmentally degraded for future food production, sustainability in the humid tropics is placed at risk. These concerns are becoming the focal points of the preservation programs and research efforts of regional and international agricultural research centers. Efforts are being made to preserve lowland areas that have unique qualities. The Chitwan National Forest in Nepal is one of the few lowland rain forests successfully protected from development pressure. It constitutes a rich source of biological diversity in undisturbed Asian lowland, high-productivity ecozones. Further development of the Chitwan area for agriculture has so far been rejected.

Throughout the humid tropics, efforts are also being made to

Front Matter (R1-R16)

Executive Summary (1-18)

Part One (19-20)

1 Agriculture and the Environment in the Humid Tropics (21-65)

2 Sustainable Land Use Options (66-137)

3 Technological Imperatives for Change (138-158)

4 Policy-Related Imperatives for Change (159-191)

References (192-214)

Appendix: Emissions of Greenhouse Gases from Tropical Deforestation and Subsequent Uses of the Land (215-260)

Part Two: Country Profiles (261-264)

Brazil (265-351)

C te d (352-392)

Indonesia (393-439)

Malaysia (440-482)

Mexico (483-548)

The Philippines (549-624)

Zaire (625-658)

Glossary (659-674)

Authors (675-678)

Index (679-704)