Slash-and-burn agriculture is a form of shifting cultivation in agriculture that involves the cutting and burning of plants in a forest or woodland to create a field called a swidden. The process begins with cutting down the trees and woody plants in a given area. The downed vegetation, or "slash", is left out to dry, usually right before the rainiest part of the year. The biomass is then burned, resulting in a nutrient-rich layer of ash which increases soil fertility and temporarily eliminates weeds and pests. After about three to five years, the plot's productivity decreases due to depletion of nutrients along with weed and pest invasion, causing farmers to abandon the plot and move 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 Bangladesh and India, the practice is known as jhum or jhoom.
A rough estimate says that about 200–300 million people worldwide use slash-and-burn agricultural techniques. Slash-and-burn causes deforestation and habitat loss. Ashes from the burnt trees help farmers by providing nutrients for the soil. While slash-and-burn agriculture has historically been sustainable in areas with low population density, increasing populations have accelerated the rate of deforestation, depleting the Earth's carbon reservoirs.
