Slash and burn agriculture

Also known as swidden cultivation or shifting cultivation , slash-and-burn agriculture is a primitive agricultural system in which sections of forest are repeatedly cleared, cultivated, and allowed to regenerate over a period of many years. This kind of cultivation was used in Europe during the Neolithic period, and it is still widely used by indigenous peoples and landless peasants in the tropical rain forests of South America.

The plots used in slash-and-burn agriculture are small, typically 1–1.5 acres (0.4–0.6 hectare). They are also poly-cultural and polyvarietal; farmers plant more than one crop on them at a time, and each of these crops may be grown in several varieties. This helps control populations of agricultural pests. The cutting and burning involved in clearing the site releases nutrients which the cultivated crops can utilize, and the fallow period, which usually lasts at least as long as 15 years, allows these nutrients to accumulate again. In addition to restoring fertility, re-growth protects the soil from erosion .

Families and other small groups practicing slash-and-burn agriculture generally clear one or two new plots a year, working a number of areas at various stages of cultivation at a time. These plots can be close to each other, even interconnected, or spread out at a distance through the forest, designed to take advantage of particularly fertile soils or to meet different needs of the group. As the nutrients are exhausted and productivity declines, the areas cleared for slash-and-burn agriculture are rarely simply abandoned; the fallow period begins gradually, and species such as fruit trees are still cultivated as the forest begins to reclaim the open spaces. The forest may contain originally cultivated species that still yield a harvest many years after the plot has been overgrown.

Although this system of agriculture was practiced for thousands of years with relatively modest effects on the environment , the pressures of a rapidly growing population in South America have made it considerably less benign. Population growth has greatly increased the number of peasants who do not own their own land; they have been forced to migrate into the rain forests, where they subsist practicing slash-and-burn agriculture. In Brazil, the number of farmers employing this system of agriculture has increased by more than 15% a year since 1975. A recently released report by the United Nations Population Fund has emphasized the destruction this system can cause when practiced on such a large scale and identified it as a threat to species diversity.

See also Agricultural revolution; Agricultural technology; Agroecology

[Douglas Smith ]