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.
History Historically, slash-and-burn cultivation has been practiced throughout much of the world. Fire was already used by hunter-gatherers before the invention of agriculture, and still is in present times. Clearings created by the fire were made for many reasons, such as to provide new growth for game animals and to promote certain kinds of edible plants. During the Neolithic Revolution, groups of hunter-gatherers domesticated various plants and animals, permitting them to settle down and practice agriculture, which provided more nutrition per hectare than hunting and gathering. Some groups could easily plant their crops in open fields along river valleys, but others had forests covering their land. Thus, since Neolithic times, slash-and-burn agriculture has been widely used to clear land to make it suitable for crops and livestock. Large groups wandering in the woodlands was once a common form of society in European prehistory. The extended family burned and cultivated their swidden plots, sowed one or more crops, and then proceeded on to the next plot.
Technique
Slash-and-burn fields are typically used and owned by a family until the soil is exhausted. At this point the ownership rights are abandoned, the family clears a new field, and trees and shrubs are permitted to grow on the former field. After a few decades, another family or clan may then use the land and claim usufructuary rights. In such a system there is typically no market in farmland, so land is not bought or sold on the open market and land rights are traditional. In slash-and-burn agriculture, forests are typically cut months before a dry season. The "slash" is permitted to dry and then burned in the following dry season. The resulting ash fertilizes the soil and the burned field is then planted at the beginning of the next rainy season with crops such as rice, maize, cassava, or other staples. This work was once done using simple tools such as machetes, axes, hoes and shovels.
Benefits and drawbacks
This system of agriculture provides millions of people with food and income. It has been ecologically sustainable for thousands of years. Because the leached soil in many tropical regions, such as the Amazon, are nutritionally extremely poor, slash-and-burn is one of the only types of agriculture which can be practiced in these areas. Slash-and-burn farmers typically plant a variety of crops, instead of a monoculture, and contribute to a higher biodiversity due to creating mosaic habitats. The general ecosystem is not harmed in traditional slash-and-burn, aside from a small temporary patch. This technique is most unsuitable for the production of cash crops. A huge amount of land, or a low density of people, is required for sustainable slash-and-burn. When slash-and-burn is practiced in the same area too often, e.g., because the human population density has increased to an unsustainable level, the forest will eventually be destroyed.
Regionally
Asia
Tribal groups in the northeastern Indian states of Tripura, Arunachal Pradesh, Meghalaya, Mizoram and Nagaland and the Bangladeshi districts of Rangamati, Khagrachari, Bandarban and Sylhet refer to slash-and-burn agriculture as podu, jhum or jhoom cultivation. The system involves clearing land, by fire or clear-felling, for economically important crops such as upland rice, vegetables or fruits. After a few cycles, the land's fertility declines and a new area is chosen. Jhum cultivation is most often practiced on the slopes of thickly-forested hills. Cultivators cut the treetops to allow sunlight to reach the land, burning the trees and grasses for fresh soil. Although it is believed that this helps fertilize the land, it can leave it vulnerable to erosion. Holes are made for the seeds of crops such as sticky rice, maize, eggplant and cucumber. After considering jhum's effects, the government of Mizoram has introduced a policy to end the method in the state. Vietnam is home to a diverse range of ethnic groups. Some of these groups form primarily rural communities that reside far from the larger cities of the country, living on swidden fields where slash-and-burn agriculture is still in regular use as a part of everyday life.
Americas
Some American civilizations, like the Maya, have used slash-and-burn cultivation since ancient times. Native Americans in the United States also used fire in agriculture and hunting. In the Amazon, many peoples such as the Yanomami Indians also live off the slash and burn method due to the Amazon's poor soil quality. Indigenous peoples in what is now modern-day Brazil also utilized slash-and-burn agriculture as land management in the Atlantic Forest prior to European colonization.
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