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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 México 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 Petén, 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 Petén, 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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