slashburn
SLASH AND BURN AGRICULTURE
The practice of slash-and-burn agriculture consists of clearing plots from the forest and allowing
the cut vegetation to dry, then burning, and finally planting crops in the ashes (Figure 1). Plots are
used for a few years and then are gradually abandoned to natural vegetation for fallow periods
(periods between plantings) of up to 20 or more years. In some areas where there is too much rain
or insufficient vegetation for a good burn, the slashed vegetation is left to decompose on its own and
cultivated after a long fallow.
Figure 1. An Amazonian rainforest being burned to clear
plots for agricultural uses.
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Although it has become relatively publicized, slash-and-burn agriculture is far more important
than most people realize. According to recent estimates, slash and burn is practiced by 240 to 500
million people on nearly one-half of the land area of the tropics (Figure 2) .
Figure 2. An Amazonian practicing slash and burn
agriculture.
Sponsel, Leslie L. 1995. Indigenous Peoples & the
Future of Amazonia, p. 26.
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slashburn
Over centuries, traditional farmers developed slash and burn agriculture systems as a solution to
poverty, soil depletion problems, and managing pests. Burning tends to reduce losses from disease
and other pests. In addition, the clearing of small plots permits easy migration of biological control
agents, such as insect parasites and predators, from the surrounding forest.
Unfortunately, the system often requires as much as 15-30 hectares to feed one person due to the
lengthy fallow period generally required. On steep slopes or under great population pressure, where
the number of people the land has to support becomes so great that the fallow periods are greatly
reduced, the system can become destructive. However, some crops exhibit an incomplete fallow
period and continue to produce harvests long after the natural vegetation begins to return.
One of the most important criteria of evaluating slash-and-burn agriculture is to determine the
various reasons that people abandon their plots after only a few seasons (Figure 3) . Many
agronomists suggest that the nutrients supplied by the ash from burning are exhausted by crops and
weeds and thus lack of nutrients cause abandonment. Others state that weed infestations are the
primary cause because labor to weed often outweighs labor required to clear a new plot. Plant
pathogens may also contribute to plot abandonment. A final possibility is the fact that burning
reduces mycorrhizal populations over time, which may lead to crops decreasing in quality after a
few years. Essentially, it is the long fallow period required that causes the slash-and-burn system to
become destructive except at low population densities. This has fueled the search for finding
sustainable alternatives to slash-and-burn.
Figure 3. An abandoned land plot that was previously
used for slash and burn agriculture.
Sponsel, Leslie L. 1995. Indigenous Peoples & the
Future of Amazonia, p. 25.
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slashburn
Some other criteria important to evaluating slash-and-burn are its effects at a variety of
organizational levels. Animal species may be harmed or even destroyed as their habitats are ruined
by the fires of slash-and-burn. The burning of forest plots may trap and isolate animals (and
unsuspecting people, for that matter!). Also, the continuous fires produce a large amount of smoke
and ash which travels through the air and water to be deposited on plants and in soil (refer to Figure
2). People native to the Amazon are most likely familiar with the burning practices but may be
unprepared for the large-scale fires that are being started by more business-oriented settlers in
several areas of the basin. There have been numerous cases of slash-and-burn that grew to be
disastrous as fires raged uncontrollably, as some 2,000 to 3,000 runaway forest fires are recorded
each year in the Amazon. One spreading fire eventually covered an area 400 x 600 km, as the
selective farming of the area left acres of drying slash, making it especially vulnerable to attack by
fire. Finally, fires induced in some areas have reduced or spoiled the vital moisture and water
supplies of the Amazon Rainforest, leaving the forest ecosystem forever changed.
Figure 2. A smoke and ash cloud from tropical slash
and burn as it dissipates into the atmosphere.
Sponsel, Leslie L. 1995. Indigenous Peoples & the
Future of Amazonia, p. 72.
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