Slash-and-burn is an agricultural technique which involves cutting and burning of forests or woodlands to create fields. It is subsistence agriculture that typically uses little technology or other tools. It is typically part of shifting cultivation agriculture, and of transhumance livestock herding.[1]
There are an estimated 250 million slash-and-burn farmers across the world.[2] In 2004 it was estimated that, in Brazil alone, 500,000 small farmers were each clearing an average of one hectare of forest per year. The technique is not sustainable beyond a certain population density because, without the trees, the soil quality soon becomes too poor to support crops. The farmers have to move on to virgin forest and repeat the process. Methods such Inga alley farming have been proposed as an alternative to this ecological destruction.[3]
Contents |
In slash-and-burn agriculture, forest will typically be 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 crop such as upland rice, maize, cassava, or other staple crop. Most of this work is typically done by hand, using machetes, axes, hoes, and other such basic tools.
Slash-and-burn fields will typically be used and "owned" by a family until the soil is exhausted. At this point the "ownership" rights are abandoned, and the family will clear a new field, and the forest is permitted to grow on the old 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, and land is not bought and sold in the open market. Such rights are "traditional."
Historically, slash-and-burn cultivation was practiced throughout much of the world, in grasslands as well as woodlands. In regions which industrialized, including Europe and North America, the practice was abandoned over the past few centuries as market agriculture was introduced, and land came to be owned. For example, slash-and-burn agriculture was initially practiced by European pioneers in North America like Daniel Boone and his family who cleared land in the Appalachian Mountains in the late 18th and early 19th Centuries.[4] However, the land of such slash-and-burn farmers was eventually taken over by modern systems of land tenure which focus on the long-term improvement of farmland, and discourage the older subsistence practices associated with slash-and-burn agriculture.
Today the term "slash-and-burn" is mainly associated with tropical rain forests. Slash-and-burn techniques are used by between 200 and 500 million people worldwide.[5]
Older English terms for slash-and-burn include assarting and fire-fallow cultivation.
Slash-and-burn is a specific functional element of certain farming practices, often shifting cultivation systems. In some cases such as parts of Madagascar, as well as many other places, slash-and-burn may have no cyclical aspects (e.g., slash-and-burn activities can render soils incapable of further yields for decades), or may be practiced on its own as a single cycle farming activity with no follow on cropping cycle. Shifting cultivation normally implies the existence of a cropping cycle component, where as slash-and-burn actions may or may not be followed by cropping. Slash-and-burn is typically a type of subsistence agriculture, and not focused by the need to sell crops in world markets. Rather, planting decisions are made in the context of needs of the family or clan for the coming year.[6]
During the Neolithic Revolution, which included agricultural advancements, groups of hunter-gatherers domesticated various plants and animals, permitting them to settle down and practice agriculture which provides more nutrition per hectare than hunting and gathering. This happened in the river valleys of Egypt and Mesopotamia. Due to this decrease in food from hunting as human populations increased, agriculture became more important. Some groups could easily plant their seeds in open fields along river valleys, but others had forests blocking their farming land. In this context, humans used slash-and-burn agriculture to clear more land, and make it suitable for their plants and animals. Thus, since Neolithic times, slash-and-burn techniques have been widely used for converting forests into crop fields and pasture.[7] Fire was used before the Neolithic as well, and by hunter-gatherers up to present times. Clearings created by fire were made for many reasons, such as to draw game animals and to promote certain kinds of edible plants such as berries. This method was also used to prepare soil for planting crops and making the soil fertile by mixing the ashes with the soil.
Although a solution for overpopulated tropical countries where subsistence agriculture may be the traditional method of sustaining many families, the consequences of slash-and-burn techniques for ecosystems are almost always destructive. This happens particularly as population densities increase, and as a result farming becomes more intensively practiced. This is because as demand for more land increases, the fallow period by necessity declines. The principal vulnerability is the nutrient-poor soil, pervasive in most tropical forests. When biomass is extracted even for one harvest of wood or charcoal, the residual soil value is heavily diminished for further growth of any type of vegetation. Sometimes there are several cycles of slash-and-burn within a few years time span; for example in eastern Madagascar the following scenario occurs commonly. The first wave might be cutting of all trees for wood use. A few years later, saplings are harvested to make charcoal, and within the next year the plot is burned to create a quick flush of nutrients for grass to feed the family zebu cattle. If adjacent plots are treated in a similar fashion, large-scale erosion will usually ensue, since there are no roots or temporary water storage in nearby canopies to arrest the surface runoff. Thus, any small remaining amounts of nutrients are washed away. The area is an example of desertification, and no further growth of any type may arise for generations.
The ecological ramifications of the above scenario are further magnified, because tropical forests are habitats for extremely biologically diverse ecosystems, typically containing large numbers of endemic and endangered species. Therefore, the role of slash-and-burn is significant in the current Holocene extinction.
Slash-and-char is an alternative that alleviates some of the negative ecological implications of traditional slash-and-burn techniques.