1、IntroductionAlso known as “shifting cultivation“, “swidden agriculture“, or simply “jhum“, slash and burn is an ancient form of agriculture practiced by between 200 and 500 million people around the world today (2006). The two key components of slash and burn agriculture are the use of fire to prepa
2、re 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
3、 a more natural state as native plant and tree species reclaim the field. As a result, over time soil nutrient levels can recover to predisturbance levels, although the resulting ecosystems often retain a preponderance of plant species used by humans. While recovering, abandoned fields (also known a
4、s “swiddens“), typically are used by humans as a source of fruits, nuts, fibers, medicinal plants, and game. Once ecosystem recovery is sufficiently advanced, the field may be used again for cultivation. Characteristics of Slash and BurnAlthough the food crops used varies with location, the sequence
5、 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
6、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. Seeds and cuttings are planted directly into the ash-covered soil. Farmers may add additional
7、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
8、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 B
9、urn Agriculture TodaySlash 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 impr
10、operly, 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 expla
11、ined 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
12、 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
13、 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 r
14、egional 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 aband
15、on 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 BurnIn contrast
16、, 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 agri
17、culture 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 s
18、pecies 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 so
19、me 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
20、 increased diversity and physical structure has been shown to have characteristics conducive to biodiversity conservation. The Future of Slash and BurnGiven sufficient quantities of land and sufficient support, some increases in the number of people practicing slash and burn type agriculture could b
21、e 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 alterna
22、tives 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 o
23、f 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 ma
24、jor 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 al
25、one 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. For the 1992 Manic Street Preachers single, see Slash n Burn.Slas
26、h and burn practices in Finland in Eno 1892Slash and burn consists of cutting and burning of forests or woodlands to create fields for agriculture or pasture for livestock, or for a variety of other purposes. It is sometimes part of shifting cultivation agriculture, and of transhumance livestock her
27、ding.Historically, the practice of slash and burn has been widely practiced throughout most of the world, in grasslands as well as woodlands, and known by many names. In temperate regions, such as Europe and North America, the practice has been mostly abandoned over the past few centuries. Today the
28、 term is mainly associated with tropical rain forests. Slash and burn techniques are used by between 200 and 500 million people worldwide.1Older English terms for slash and burn include assarting, swidden, and fire-fallow cultivation.Slash and burn is a specific functional element of certain farming
29、 practices, often shifting cultivation systems. In some cases such as parts of Madagascar, slash and burn may have no cyclical aspects (e.g., some slash and burn activities can render soils incapable of further yields for generations), or may be practiced on its own as a single cycle farming activit
30、y with no follow on cropping cycle. Shifting cultivation normally implies the existence of a cropping cycle component, whereas slash-and-burn actions may or may not be followed by cropping.Contentshide 1 Slash-and-burn defined 2 Historical background 3 Ecological implications 4 See also 5 References
31、 o 5.1 Bibliography o 5.2 Notes edit Slash-and-burn definedBurned farmland near Santa F (Veraguas Province), Panam.An area of primary or secondary forest is selected, and the vegetation is cut and allowed to dry. Large trees are often girdled and allowed to die standing. Some trees are often left st
32、anding, especially those viewed as useful, such as food producing trees like chestnuts or economically valuable trees like teak. Portions of the cut timber or saplings are often gathered to use for firewood or to make charcoal. After some period of time (a week to a few months) the residual dry vege
33、tation is burned. Plots are cultivated for a few seasons (usually one to five years) and then abandoned as fertility declines and weeds invade.Such abandoned plots often become used as pasture for livestock. If the forest is allowed to recover, pasture becomes rough pasture for a while. Recovering w
34、oodlands are sometimes treated as “fallow“ land, which means it is to be subjected to another round of slash-and-burn in the future.2Burning removes the vegetation and may release a pulse of nutrients to fertilize the soil. Ash also increases the pH of the soil, a process which makes certain nutrien
35、ts (especially phosphorus) more available in the short term. Burning also temporarily drives off soil microorganisms, pests, and established plants long enough for crops to be planted in their ashes. Before artificial fertilizers were available, fire was one of the most widespread methods of fertili
36、zation.2Slash and burn requires a relatively low human population density or a continuing supply of new “frontier“ lands, since the recovery of forests may require many decades or even human generations.Various forms of slash-and-burn have been used in nearly every forested environment, from the tem
37、perate 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. Much of the temperate forest cutting was followed by sustainable grazing or crop rotation practices. An almost total
38、conversion of forests to farmland and pasture has occurred in many temperate regions, such as England. In many tropical forests, sustainable forms of slash and burn have been practiced for millennia, but population growth and large-scale industrial logging, among other factors, have made traditional
39、 slash and burn practices less sustainable and more likely to result in catastrophic wildfires.2edit Historical backgroundDuring the Neolithic Revolution, or “new stone age revolution“ which included agricultural advancements, groups of prehistoric humans started domesticating various plants and ani
40、mals, shifting from a hunter-gatherer lifestyle toward agriculture and pastoralism. The origins of domestication are not known. One theory is that it was mainly due to the end of the last glacial period (ie. about 9-11,000 years ago), resulting in the extinction of many of prehistoric mans game, suc
41、h as the woolly mammoth. Due to this decrease in food from hunting, some groups started to turn to agriculture. Some groups could easily plant their seeds in open fields, but others had forests blocking their farming land. Since Neolithic times, slash and burn techniques have been widely used for co
42、nverting forests into crop fields and pasture.3 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.edit Ecological im
43、plicationsAlthough a dilemma for overpopulated tropical countries where subsistence farming may be the easiest method of sustaining many families, the consequences of slash-and-burn techniques to ecosystems are almost always deleterious when practiced on a large scale. The principal vulnerability is
44、 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 sp
45、an; 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
46、family zebu. 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 dese
47、rtification, 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 event.
