Slash and burn agriculture—also known as swidden or shifting agriculture—is a traditional method of tending domesticated crops that involves the rotation of several plots of land in a planting cycle. The farmer plants crops in a field for one or two seasons, and then lets the field lie fallow for several seasons. In the meantime, the farmer shifts to a field that has lain fallow for several years, and removes the vegetation by cutting it down and burning it—hence slash and burn. The ash from the burned vegetation adds another layer of nutrients to the soil, and that, along with the time resting, allows the soil to regenerate.
Slash and burn works best in low intensity agriculture, when the farmer has plenty of land that he or she can afford to let lay fallow; and it works best when crops are rotated to assist in restoring the nutrients. It has also been documented in societies where people maintain a very broad diversity of food-generation; that is, where people also hunt game, fish, and gather wild foods.
Environmental Effects of Slash and Burn
Since the 1970s or so, swidden agriculture has been described as both a bad practice, resulting in the progressive destruction of natural forests, and an excellent practice, as a refined method of forest preservation and guardianship. A recent study conducted on historical swidden agriculture in Indonesia (Henley 2011) documented the historical attitudes of scholars towards slash and burn and then tested the assumptions based on more than a century of slash and burn agriculture.
Henley discovered that the reality is that swidden agriculture can add to deforestation of regions, if the maturing age of the removed trees is much longer than the fallow period used by the swidden agriculturalists. For example, if a swidden rotation is between 5 and 8 years, and the rainforest trees have a 200-700 year cultivation cycle, then slash and burn represents one of what may be several elements resulting in deforestation. Slash and burn is a useful technique in some environments, but not in all.
A recent set of papers in a special issue of Human Ecology in 2013 suggests that the creation of global markets is pushing farmers to replace their swidden plots with permanent fields. Alternatively, when farmers have access to off-farm income, swidden agriculture is maintained as a complement to food security (see Vliet et al. for a summary).
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