In heavily forested areas, or those with little usable soil for farming, natives often turn to slash-and-burn deforestation to feed their families. This traditional farming technique involves cutting down most of the vegetation on a patch of land, then setting fire to the remainder. The resulting ashes serve as viable nutrients for future farming on the site, although only for a brief period.
People in many parts of the world have relied on slash-and-burn farming for thousands of years, and some estimates suggest it's used on half of all land in tropical areas [source: Virginia Tech]. Although this practice can serve as a successful method of agriculture in the short term, it also leads to significant problems on both local and global scales.
Each acre of land subject to slash-and-burn deforestation releases 180 metric tons of carbon into the atmosphere [source: MIT]. This carbon eventually reaches the Earth's ozone layer, where it contributes to the greenhouse effect and global warming. After this initial carbon release, slash-and-burn deforestation then packs a secondary punch to the planet, as these burned trees are no longer available to convert carbon into oxygen through photosynthesis. Forest fires and the resulting smoke also contribute to air and water pollution, and can often rage out of control, threatening the lives of people and animals. Slash-and-burn deforestation also destroys habitats and threatens ecosystems, which is particularly problematic in these tropical areas because of their unique levels of biodiversity.
For local natives, this agricultural technique represents a double-edged sword. Those who practice slash-and-burn agriculture often do so out of desperation to feed themselves and their families, and yet this technique may lead to greater risk of starvation in the near future. The ashes produced by these fires provide nutrients to sustain the land for just three to five years; after that, the land must remain fallow for a decade or more to regenerate. Without the traditional vegetation and root system, however, significant erosion occurs, and the land is unable to sustain enough nutrients to ever reach its former glory. During the rainy season, erosion may contribute to dangerous flooding, while the lack of tree cover and vegetation can make existing drought conditions worse during the dry season.
Some scientists believe that even the mighty Mayan empire succumbed to the effects of slash-and-burn farming. For years, the Mayans relied on this technique to survive in the tropical region now known as Guatemala. Scientists have determined that just before the Mayan empire fell -- around A.D. 900 -- widespread deforestation had resulted in a complete absence of tree pollen. The lack of trees in the area led to a temperature increase of roughly 6 degrees, which eventually brought about widespread drought. The drought signaled the end for the Mayans [source: NASA].
When loggers need to clear a large area of forested land quickly, they often institute a practice known as slash-and-burn deforestation, where large chunks of the forest are cut down and then burned, clearing the land for use in farming and development. These practices are particularly dangerous to rainforest ecosystems, because many of the native plants require a delicate balance of nutrients, sunlight and moisture that they cannot have without the original trees still in place. After the heavy rains wash away what little is left of the minerals in the soil, these areas are left almost entirely dead.
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