Preface

Overgrazing, fuelwood collection, uncontrolled burning, the unregulated exploitation of forest products, the growth of transportation networks, agricultural expansion into marginal areas, major social and economic changes are but some of the factors that have contributed to the degradation of tropical and subtropical rangelands. Periodic drought has intensified the impact of vegetation loss, and it appears that this loss may, in turn, prolong drought. Because rangelands comprise a substantial percentage of the earth's surface and support millions of human beings, it is critical to understand the complex causes of this cycle of drought and degradation, and to ensure that socially, economically, and scientifically appropriate measures be formulated and implemented to stem degradation and increase the productivity of rangelands.

The areas affected include some of the most vulnerable ecosystems in the world. For example, once disturbed, dryland ecosystems often require decades, or even centuries, to regain productivity. Nevertheless, there can be no moratorium on the use of such "fragile" lands; their products are vitally important. Although this report focuses upon problems of range improvement in Africa and Asia, many of the observations and recommendations could be applied to the tropics and subtropics of Latin America as well.

The panelists and other individuals responsible for preparing this report have no illusions regarding the case with which productivity can be restored to the world's rangelands. The areas are vast, and measures that could improve them are characteristically costly in terms of labor or capital. Rehabilitation efforts are further affected by social and political considerations.

This report takes a broad perspective. It focuses on the principles of range management by describing various indigenous adaptations to specific Old World ecosystems, and by discussing how experience elsewhere can complement indigenous knowledge. It also outlines techniques for assessing the condition of rangeland vegetation. Although the report to some extent draws upon North American experience, its authors fully acknowledge the limitations of this experience in addressing degradation problems in the tropics and subtropics. Nevertheless, this experience can usefully illustrate the application of basic principles, which the panel hopes will stimulate local research. What is needed is a basic appreciation of indigenous adaptations, a knowledge of local socioeconomic and environmental change over time, and innovation solidly based on an understanding of ecological principles.

Rangelands that are "common property" are particularly difficult to manage because of the frequent breakdown of organizations and institutions responsible for their welfare. Successfully managed rangelands characteristically benefit from some form of local control Therefore, case studies that describe successful approaches are also provided.

This report complements More Water for Arid Lands, published by the National Academy of Sciences in 1974, which describes littleknown, but promising, small-scale technologies for the use and conservation of scarce water supplies in arid areas. The Improvement of Tropical and Subtropical Rangelands is the third report to appear in the series Resource Management for Arid and Semiarid Regions. Other titles include Environmental Change in the West African Sahel and Agroforestry in the West African Sahel.