ditional systems are diverse in their particular adaptations, they share many traits: high retention of nutrients; maintenance of vegetative cover; a high level of diversity of crops and crop varieties; complex cropping patterns and time frames; and the integration of domestic and wild animals within the agroecosystem.

Shifting cultivation (also known as swidden, slash-and-burn, or slash-and-mulch agriculture) remains in wide use throughout the humid tropics. It is practiced on about 30 percent of the world's arable soils and provides sustenance to more than 300 million people and additional millions of migrants from other regions (Andriesse and Schelhaas, 1987). As traditionally practiced, shifting cultivation protects the resource base through efficient recycling of nutrients, conservation of soil and water, diversification of crops, and the incorporation of long fallow periods in the cultivation cycle. Fallows accumulate nutrients in their biomass and control weeds.

Traditional shifting cultivation systems are being disrupted, modified, and replaced as population pressures rise and as migrants unfamiliar with the humid tropics or indigenous land use practices attempt to farm newly cleared land. Typically, this results in shortened fallow periods, fertility decline, weed infestation, disruption of forest regeneration, and excessive soil erosion.

Monocultural systems have been successfully introduced over large areas of the humid tropics. Some of the more fertile soils already support monocultural production of coffee, tea, bananas, citrus fruits, palm oil, rubber, sugarcane, and other commodities produced primarily for export. However, the social and economic characteristics of monocultural crop and plantation systems are of concern in many countries where they are important land uses. While they provide productive employment, they often outcompete and, thus, discourage investment in domestic food crop production. At the same time, they occupy most of the high-quality agricultural land, although this is less true in the Asian humid tropics. They often entail concentrated ownership of large areas of land (either in the private sector or by the government), creating social and political instability, especially in densely populated countries. Where these land ownership patterns are pervasive, small-scale farmers who wish to continue farming have no other option but to move toward primary forests and marginal lands (rice farmers are an important exception in that rice production is carried out largely on long-established small farms). Fluctuations in world market prices of the commodities these systems produce, as well as the fertilizers and pesticides on which they depend, make monocultural production more vulnerable to political and macroeconomic trends than small-scale farming. This is evident,