Swidden Agriculture

Swidden agriculture—a more expansive form of slash-and-burn agriculture—is a type of shifting cultivation that entails the cutting and drying of all vegetation from a forest patch until fire can properly take hold. Following burning, the resultant ash provides the swidden farmer with a sufficient nutrient base from which to farm for up to four years. The burning process also removes potentially damaging pests from the plot. After the nutrients have been exhausted from the swidden plot, the farmer moves to an adjacent plot of forest land and repeats the entire process of cutting, drying, burning, planting, harvesting, and abandoning again.

Swidden agriculture has been practiced on most forest types throughout the globe but currently is almost exclusively used in tropical forests. Tropical forests are not suitable for the type of conventional agriculture commonly practiced in temperate climates because of their soils. Tropical forest oxisol and ultisol soils are very old and largely devoid of essential nutrients required for farming crops. Nutrient cycling in tropical biomes is vastly different than other forest types. In the tropics, the nutrient base is bound up almost exclusively in living trees and plants and in the decaying wood and vegetation that litter the forest floor—which can exceed a meter in depth. The swidden farmer cuts and burns a forested plot to capture a portion of the nutrient base bound up in the vegetative material to nourish future crops.

In tropical forest systems, with few cultivators compared with vast expanses of forest land, and with small farmed plots, slash-and-burn agriculture is relatively benign, as the surrounding forests quickly encroach on the farmed plot following abandonment. Indigenous Amazonian populations have practiced this type of agriculture for centuries with minimal deleterious effects. This method of farming, when practiced with properly spaced small plots, can even increase biodiversity, as it mimics natural forest openings created when large overstory trees die and fall, taking with them large sections of understory vegetation. Small openings within the forest interior allow early successional species that cannot tolerate the high-shade conditions of old growth tropical forests to reestablish themselves. Furthermore, forest openings provide edge effects that increase the variety of plant and animal food resources for some tropical forest herbivores and carnivores.

However, when human populations expand in tropical environments and the swidden plots are large, the continued practice of this form of agriculture can be devastating to the biological integrity of tropical forests. When colonialists practice swidden agriculture in its more expansive form, it takes long periods of time for these lands to recover for a variety of reasons. Because tropical forest soils are nutrient poor and have been further impoverished following successive rotations of conventional cropping, they cannot easily support [Page 425]tropical revegetation. Furthermore, the loss of a protective cover of forest detritus, root systems, and vegetation subjects tropical soils to bleaching by the strong tropical sun, which can destroy essential rhizomal systems. Frequent tropical rains can also remove remaining topsoil from the abandoned patch. When a combination of insults is foisted on tropical forests, it might take from many decades to more than a century before a swidden-farmed plot will return to its preharvest state.

...