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SOME PRINCIPAL AGENTS OF TROPICAL DEFORESTATION
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Forest is cut and dried, in preparation for burning.
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Shifting Cultivation
Shifting cultivation--also known as swidden agriculture or slash-and-burn farming, and in M�xico and Central America, as "milpa" agriculture--is the predominant style of farming in many portions of the globe's humid
tropics, supporting millions of families worldwide. And in fact, this style of farming was once commonly practiced in Europe and North America as well. Myers (1980) states that, "By far the
most important factor in conversion of tropical moist forests (TMF) appears to be the forest farmer." The importance of shifting cultivation as an agent in deforestation varies regionally, but in many parts of Latin
America, Myers' statement appears accurate. Certainly in the Maya Forest region, our observations concur that shifting agriculture is among the primary agents of forest conversion.
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Burning of the dried slash is hot
and smoky, but an exciting event.
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Shifting agriculture takes place predominantly in forest environments, and burning of the forest biomass in part provides nutrients for farming. The salient feature of shifting agriculture is this--that a given plot of ground
is farmed for a year or more (depending on local conditions) and then is abandoned to secondary succession for a few to many years before again being felled and planted.
In our study area, the process takes the following form. A peasant farmer (often with sons or hired help) fells a couple
of hectares (four
to five acres) of primary or successional forest during the dry season. Usually this is done strictly by axe and machete, with chain saws rarely employed. After drying for a month or more, toward the end of the dry season (April
or May) the drying slash is burned. Afterward, corn is planted by making holes with a pointed planting stick, and dropping the kernels in--there is no use of tractor-drawn nor beast-drawn plows or other machinery.
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With the use of a digging stick, corn or
other crops
will be planted among the
charred trunks and logs.
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The crop is strictly rain fed, and in dry years, crop failures result in widespread hardship. In northern Pet�n, two corn crops are often grown during the first year after field preparation, and the field is then abandoned
to fallow.
During the first crop, planted in May or June, just before the onset of rains, weeding is generally not necessary. Prior to planting the second crop (October or November), farmers traditionally needed to spend several days
chopping tall weeds; today this weed control is often achieved by use of herbicides applied using a back-pack sprayer.
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Corn grown in a swale that recently
supported "hill-base" forest.
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After two crops, the field is normally abandoned and the farmer prepares another site for planting--either from primary forest, or from successional growth on fallowed fields used in the past.
Presumably under low human population densities, fields were often fallowed for many years. Today however, in our study area, the average fallow time before a field is again farmed is about 4.2 years, and rarely more than 8
years. On average, each farming family in our study area cut down 0.63 hectares of primary forest and 1.8 hectares of successional forest each year for farming purposes.
Why do farmers abandon a field to move on to another? It was once believed that this had strictly to do with decline of soil fertility under cultivation. Today it is realized that this is part of the answer, but that the increase
of pests, especially weeds, under cultivation, is also a major part of the reason. As weeds invade a field and soil fertility drops, the balance of labor versus yield quickly reaches the point at which it is more economical
for a farmer to leave one field and move on to another that is under forest cover--so long as forested land is readily available at a low cost or at no cost.
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Farmer inspects ear of corn.
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Once a field has been fallowed for several years, secondary succession provides a natural weed-suppression service, and for the first few months after felling and burning, weed problems are manageable. Soon after, however,
fast-growing weeds including grasses make inroads, causing diminished corn yields and/or demanding excessive labor inputs for weeding.
The Role of Shifting Cultivation in Tropical Deforestation
This farming technology is largely free of reliance on fossil fuel inputs, and hence is more sustainable, in a fashion, than is farming as practiced today in the U.S. corn belt. Moreover, under low human population densities,
so long as large areas of old-growth forest remain in the landscape, this farming technology is readily compatible with goals of biodiversity conservation--in fact, regional biodiversity is probably maximized in such landscapes,
so long as some large tracts of mature forest remain.
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This area in southern Pet�n, Guatemala has been
farmed so long and hard that essentially no
forest-like vegetation
remains in the landscape.
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However, under today's human population pressure and existing social arrangements, fallow periods are short, and in most areas of the humid tropics, more pristine forest is brought into the farming cycle each year. Forest felled
for farming today will not retain truly old-growth characteristics in our life times. Moreover, since forest is required for this style of farming, it takes place, by definition, within remaining forested areas. In many cases
officially protected forest reserves are the locus of much current slash-and-burn farming, as these lands are often not adequately patrolled to prevent such incursions. It is difficult to escape the impression that such protected
areas are in essence serving as "relief valves" for social and demographic pressure; so long as landless peasants are able to find a tract of forest and squat for a time, growing a corn crop each year, social pressures
remain below the threshold that might produce revolution or other serious political ferment. Indeed, speaking of the conversion of Amazonian forests into cropland and pasture, Southgate (1998, p. 4) states that "increased agricultural output was never the main purpose of colonization efforts. Instead, the primary goals were to ease demographic pressure in more densely
populated regions and to solidify national territorial claims."
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