hectare yields over five years roughly 200 percent higher than systems established by colonists and 175 times that of livestock (Hecht, 1989a:173).

Agricultural systems based on indigenous models can be profitable in a market economy. Japanese colonist smallholders in the Amazon have created complex systems that prevent soil degradation and tolerate soil acidity and aluminum toxicity better than annual crops. These systems involve polycultures of mixed perennial and annual crops that are transformed, over time, into polycultures of mixed perennials. Commercial quantities of black pepper, cacao, passion fruit, rubber, papaya, eggs, and pumpkins and other vegetables are produced (Subler and Uhl, 1990). Into this sustainable, intensive agroforestry system, the Japanese farmers often incorporate fish culture and chicken and pig production and use waste or refuse from one operation as inputs to other operations (Uhl et al., 1989).

The knowledge about environmental adaptation resident in indigenous social groups depends, of course, on the survival of these groups. Development strategies that destroy the forests can undermine the ability to mitigate or respond to global change by threatening local sociocultural systems based on sustainable, noninvasive strategies of using the land. In the Amazon, the newly expanding, extensive land uses are not compatible with indigenous Indian systems of gathering, long-fallow cultivation, fishing, and hunting and also threaten the subsistence of some 2 million small-scale extractors who collect rubber, nuts, resins, palm products, and medicines while practicing small-scale farming and foraging. Current issues in the Brazilian policy debate that will affect the viability of indigenous groups include the implementation of reserves on which these groups collectively determine resource exploitation (Hecht and Cockburn, 1989), institutions governing the enclosure of public land for unrestricted private uses, and various types of park or biosphere areas with protected wilderness and some degree of zoned multiple use (Poole, 1989:43).

Indigenous sociocultural systems that have adapted to highly variable environments may offer lessons for improving the robustness of social systems to environmental changes outside of past experience. The adaptation in the Sahel points to the importance of diversified sources of cash and subsistence in allowing local groups to adapt to environmental change with limited human cost. An instructive counterexample may be the American Great Plains, where a new generation of settlers between the 1890s and 1920s developed an agricultural system poorly adapted to the area's vari-

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