Human-Environmental Influences and Interactions in Shifting Agriculture

A good deal of agriculture in the tropics is practiced on a rotational basis on environmentally fragile land (Gradwolh and Greenberg, 1988). Shifting, or rotational, agriculture is a feature of areas with low population densities, and as rural populations have grown in the past two generations, fallow period, and hence rotational cycles, have shortened, and some areas of rotational practice have come under continuous cultivation!. Sometimes, but not universally, this intensification has been supported by the use of chemical fertilizers and pesticides. Concerns have been expressed for accompanying erosion, soil and water quality deterioration, deforestation, local and regional climatic changes (Smith, 1982), and even global warming as the use of these lands is intensified (Hall and Uhlig, 1991). This paper studies the influences of a number of social phenomena on two major characteristics of shifting agriculture: the length of the rotational cycle and the total extent of land rotationally cultivated. As external influences on these shifting cultivation practices, we examine population changes, price changes, and interest rates. To get a coherent and consistent perspective on these cultivation practices and how they are influenced by these events, we develop a simple model of the behaviour of shifting cultivators. Their demand for land is derived from profit maximization while the supply of land is a function of economic accessibility offered by transportation capabilities.