Slash-and-burn agriculture, also called fire-fallow cultivation, is a farming method that involves the cutting and burning of plants in a forest or woodland to create a field called a swidden. The method begins by cutting down the trees and woody plants in an area. The downed vegetation, or "slash", is then left to dry, usually right before the rainiest part of the year. Then, the biomass is burned, resulting in a nutrient-rich layer of ash which makes the soil fertile, as well as temporarily eliminating weed and pest species. After about three to five years, the plot's productivity decreases due to depletion of nutrients along with weed and pest invasion, causing the farmers to abandon the field and move over to a new area. The time it takes for a swidden to recover depends on the location and can be as little as five years to more than twenty years, after which the plot can be slashed and burned again, repeating the cycle. In India, the practice is known as jhum or jhoom.
Slash-and-burn can be part of shifting cultivation, an agricultural system in which farmers routinely move from one cultivable area to another. It may also be part of transhumance, the moving of livestock between seasons. A rough estimate is that 200 million to 500 million people worldwide use slash-and-burn. In 2004, it was estimated that in Brazil alone, 500,000 small farmers each cleared an average of one hectare (2.47105 acres) of forest per year. The technique is not scalable or sustainable for large human populations. Methods such as Inga alley cropping and slash-and-char have been proposed as alternatives which would cause less environmental degradation.
A similar term is assarting, which is the clearing of forests, usually (but not always) for the purpose of agriculture. Assarting does not include burning.