Slash-and-Burn Agriculture

The slash-and-burn method differs from a much more ancient system known as shifting cultivation. Shifting cultivation has long been used by humans for subsistence agriculture in tropical forests worldwide, and variants of this system are known as swidden in Africa, as caingin in the Philippines, as milpa in Central America, and by other local names elsewhere. The major difference between the slash-and-burn system and shifting cultivation is in the length of time for which the land is used for agriculture. In the slash-and-burn system, the conversion is long-term, often permanent. Shifting cultivation is a more ephemeral use of the land for cultivation.

Slash-and-burn agriculture in Peru. Photograph by Asa C. Thoresen. National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.

Shifting cultivation begins when a small area of tropical forest, typically less than one to several acres, is cleared of trees and shrubs by an individual farmer. The biomass is burned, and the site is then used to grow a mixture of agricultural crops for a few years. After this time, vigorous developments of weeds and declining fertility due to nutrient losses require that the land be abandoned for a fallow period of 15-30 years or more. Meanwhile new tracts of forest are successively cleared and cultivated for several years. Clearly, the shifting cultivation system is only sustainable if the population density is small, and if the major goal of agriculture is subsistence, rather than market farming.

Because the slash-and-burn system is a longer-term, often permanent conversion of the tropical forest into agriculture, without an extended fallow period, its associated environmental problems tend to be more severe than those that are normally caused by the smaller scale, shifting cultivation systems. However, severe environmental problems can also be caused if too many people practice shifting cultivation in a small area of forest.