Slash and burn
Slash and burn practises, Also known as shifting cultivation, swidden agriculture, or simply jhum, is an ancient form of agriculture practiced by 200 to 500 million people around the world currently. The two key components of slash and burn agriculture are the use of fire to prepare fields for cultivation and the subsequent abandonment of those fields as productivity declines. The inevitable decline in productivity is a result of the depletion of soil nutrients and also a result of the invasion of weed and pest species.
Once abandoned however, fields are allowed to return to a more natural state as native plant and tree species reclaim the fieldd. As a result, over time soil nutrient levels can recover to pre disturbance levels, although the resulting ecosystems often retain a preponderance of plant species used by humans. Slash and burn contributes significantly to global carbon dioxide emissions, and also reduces forest extent useful as a carbon sink. While recovering, abandoned fields (also known as swiddens), typically are used by humans as a source of fruits, nuts, fibers, medicinal plants, and game. When ecosystem recovery is sufficiently advanced, the field may be used again for cultivation; however, in many cases, soil loss is so high that recovery time may be measured in millennia.
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Characteristics of Slash and Burn
Although the food crops used varies with location, the sequence of events in slash and burn agriculture are very similar around the world. Farmers begin to prepare a field by cutting down many of the trees and woody plants in an area. Trees that provide fruits, nuts, building materials or other useful products may be spared. The downed vegetation or "slash" is allowed to dry until right before the rainiest part of the year, at which time the slash is burned converting biomass into nutrient-rich ash. Burning also temporarily eliminates most pest and weed species. The burning produces signicant amounts of air pollution, especially the greenhouse gas, carbon dioxide, and the harmful air pollutant, particulate matter. Seeds and cuttings are planted directly into the ash-covered soil. Farmers may add additional slashed vegetation from offsite as mulch which further enhances soil fertility while protecting the soil from erosion. Mulch made from the cuttings of plants which contain natural insecticides such as Piper nigrum may also be used to protect crops from pest species. Fields may be weeded one or more times, but inevitably, weed and pest species take their toll on productivity. Depending upon location, fields may be cultivated for three to five years, and again, depending upon location, be allowed to recover for as little as five to over twenty years before being cut and burned again.
Slash and Burn Agriculture Today
Slash and burn agriculture is particularly important throughout the tropics where, when done properly, it can provide people with a secure source of food and income and has been shown to be sustainable over long periods of time. Many critics point out however that when done improperly, slash and burn agriculture can quickly degrade large areas of forest which do not recover. This realization has led to a great difference in opinion between advocates and critics of the proper role, if any, of slash and burn agriculture in development. This difference in opinion may be explained by an examination of how slash and burn agriculture is being used today. In those areas of the tropics which have experienced the rapid influx of settlers such as the states of Acre and Rondonia in Brazil, slash and burn agriculture has contributed to the rapid loss of forest cover. The problem here (and in most places throughout the tropics) however is not slash and burn agriculture itself, but the rapid increase in the number of people cutting and burning the forest in order to produce food for themselves and their families. In addition, new settlers ofter lack several key resources and skills needed to successfully and sustainably use slash and burn agriculture. These include (1) a lack of detailed knowledge of local soils, climate, and ecosystems, (2) a lack of agricultural knowledge and skills (3) a lack of credit and technical support, and (4) poor integration with local and regional economies. To these problems may be added the issues of secure land tenure and access to sufficiently large areas in which to practice slash and burn agriculture. All too often, settlers enter an area, clear the forest, cultivate crops for a short period of time, and then are forced to abandon their farms because they cannot produce enough food and income to support themselves. The result is that these settlers may be forced to sell their land to larger landowners, move on to another location and start over cutting and burning new forest lands.
The Benefits of Slash and Burn
In contrast, in areas which have not experienced rapid population growth and where sufficient land exists, slash and burn agriculture has proven more sustainable and about as productive as more modern, energy-intensive agricultural methods. When done properly over a sufficiently large area, slash and burn agriculture results in a mosaic of agricultural, secondary (i.e., abandoned), and primary (i.e., relatively undisturbed) ecosystems that mimic more closely natural disturbance regimes than does mechanized, modern agriculture. For example, slash and burn farmers typically plant or retain dozens of crop species in each field along with useful trees. In contrast, modern mechanized agriculture often results in large areas planted in a monocrop and requires the removal of almost all trees in order to use farm machinery. Because slash and burn fields typically incorporate many crop species and retain some tree species, slash and burn fields more closely mimic surrounding secondary and primary ecosystems in terms of both structure and diversity. Indeed, because farmers often incorporate useful trees into fields, slash and burn agriculture may be thought of as a form of agroforestry which because of increased diversity and physical structure has been shown to have characteristics conducive to biodiversity conservation.
The Future of Slash and Burn
Given sufficient quantities of land and sufficient support, some increases in the number of people practicing slash and burn type agriculture could be accommodated in places such as the Amazon. But slash and burn agriculture cannot provide a solution for the rapid population growth occurring in many tropical countries. Instead, a great deal of emphasis has been placed on finding so-called alternatives to slash and burn agriculture. These alternatives often focus on "poverty alleviation" to provide jobs, incomes, and social services to growing populations instead of encouraging poor people to relocate to forested areas and engage in slash and burn agriculture. Other alternatives include improving both the productivity and economic returns of land currently engaged in slash and burn agriculture instead of increasing the area under slash and burn cultivation. A third alternative is to increase the area devoted to modern, intensive agriculture and so grow sufficient food to feed growing populations. But these alternatives are based on major shifts in national and international policy and economics and in the case of increasing the extent of mechanized agriculture may not be possible or sustainable at all in the tropics. Nor is it likely that any or all alternative forms of agriculture will be able to provide sufficient food, let alone higher standards of living for rapidly growing human populations. Instead, it is much more likely that the future will see a continued increase in the use of slash and burn agriculture, especially wherever tropical forests remain.
See Also
- Carbon dioxide emissions
- Deforestation
- Forest Fuel Reduction
- Forests as a Carbon Sink
- Indoor Heating and Cooking
References
- *"Slash-and-burn agriculture". Encyclopaedia Britannica.
- Jones, C.D. and Cox, P.M., 2005. On the significance of atmospheric CO2 growth rate anomalies in 2002–2003. Geophysical Research Letters, 32(14).
- Seiler W, Crutzen P (1980) Estimates of gross and net fluxes of carbon between the biosphere and atmosphere from biomass burning. Climatic Change 2: 207-247.
