Slash and burn
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Slash and burn agriculture (also known more neutrally as shifting cultivation or swidden-fallow agriculture) is a agricultural system widely used in forested areas. Although it was practised historically in temperate regions, it is most widely associated with tropical agriculture today.
Agricultural plots are selected and the vegetation is cut and allowed to dry. Large trees are often girdled and allowed to die standing. After some period of time (a week to a few months) the dry vegetation is burned. Plots are cultivated for a few seasons (usually 1-5 years) and then abandoned as fertility declines and weeds invade.
Burning removes the vegetation and releases a pulse of nutrients which fertilize the soil. Ash also increases the pH of the soil, a process which makes certain nutrients (especially phosphorus) more available.
Slash and burn requires a low population density, as the recovery of forest may take decades. One of the side effects is erosion. Slash and burn has been used in different regions from the temperate coniferous forests of Northern Europe (e.g., svedjebruk in Russia, Finland, Sweden and Norway) to the tropical moist broadleaf forests of Indochina and the Amazon Rainforest.
Slash and burn agriculture is sometimes denounced as ecologically destructive, but it is not so when practiced by small populations in large forests, where fields have sufficient time to recover before again being slashed, burned, and cultivated. Problems with ecological unsustainability can arise with significant increases of population, leading to increased pressure on the land and failure to let fields lie fallow for enough time, as has been seen in the late 20th century in parts of the rainforests of Mexico and Brazil.
More efficient methods have replaced slash and burn almost everywhere. It is still practised in some isolated parts of Mexico, India and Indochina. It is common in Madagascar, where it is known as tavy.
Since the 1990s, a rise in the use of slash and burn agriculture to plant coca, marijuana and opium poppy as part of the illegal drugs trade has contributed to a yearly deforestation of more than 100,000 acres in Colombia.
See also: Milpafi:Kaskiviljely de:Brandrodung