Impact of Agriculture in the Rainforest

Impact of Agriculture in the Rainforest

COMMERCIAL AGRICULTURE

Agricultural use of some rainforest land proves to be a failure because of the nutrient-deficient, acidic soils of these forests. Nevertheless, many commercial agricultural projects are still carried out on rainforest lands, although many of these revert to cattle pasture after soils are depleted. Some floodplain regions, like those of the lower Amazon (várzea), are more suitable for commercial agriculture because annual floods replenish nutrient stores.

Generally forest clearers use slash-and-burn techniques to clear land, but on a much larger scale than traditional practices. Instead of burning a mere 2-10 acres (1-4 ha), agriculturalists burn hundreds to thousands of hectares. This slash-and-burn technique is generally wasteful since it is only occasionally that trees with timber value are removed before the forest is clear cut and left to dry. Following cutting, the area is burned to release nutrients locked up in vegetation and produce a layer of nutrient-rich material above the poor soils of the former tropical forest. The cleared area is quickly planted and supports vigorous growth for a few years, after which the nutrient stock is depleted and copious amounts of fertilizer are required to keep the operation viable. Fertilizer may be washed into local streams, affecting fish and aquatic life. When the use of fertilizer is deemed no longer efficient, the land is abandoned and allowed to revert to scrub. Drought-resistant grasses may move in or cattle ranchers may plant imported African grasses for cattle grazing. The land is now only marginally productive and a limited number of cattle can subsist in the area.

When the land is suitable for agriculture, generally large single cash crops like rice, citrus fruits, palms, coffee, coca, opium, tea, soybeans, cacao, rubber, and bananas are cultivated. Some of these crops are better adapted to such conditions and last longer on cleared forest lands. However, there are several problems with this type of monoculture (single crop plantations) in the tropics, besides the loss of forest. First, such planting of a single crop makes the crop highly vulnerable to disease and pests, as periodic infestations have shown in Brazil, India, and other places. In natural rainforest, widespread infestations are rare because individuals of a given species are widely dispersed. Second, the planting of monocultures can be economically risky with the price fluctuations so common in international commodities markets. Additionally, a single cold spell or drought can devastate a tremendous part of the agricultural economy.

In the state of Acre in western Brazil, farms and pastures are surrounded by large, undisturbed areas of Amazon rainforest. Since January 2005, many areas in the state have been experiencing severe drought, and the forests have become tinder dry. Since August, agricultural fires—many of them ignited in violation of a state-declared ban—have been escaping control, racing through adjacent fields and spreading into the forests. The situation deteriorated through September, and record amounts of previously undamaged rainforest may burn before the episode is over. Several NASA-funded scientists have helped the Brazilians respond to the disaster by providing daily summaries of fire detections made by satellite, aircraft, and ground observations.

These images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite show a pattern of forest and farmland east of the city of Rio Branco before (top) and after (bottom) the peak of the 2005 agricultural burning season. The images are made from visible, shortwave, and near-infrared light detected by MODIS. Bright green is unburned forest, bright red is recently burned areas, and tan is cleared, but unburned land. Next to some burned fields, the forest appears dark green, or "bruised," probably indicating places where fires escaped from fields and burned into the forest understory.

NASA images by Jesse Allen (NASA Earth Observatory) and Jeff Schmaltz (MODIS Rapid Response), text courtesy of NASA's Earth Observatory.

The cultivation of some of these crops in mountainous, watershed areas has adverse effects for the environment, notably the alteration of water cycles and erosion. In Peru, the cultivation of coca plants (containing the basic ingredient for cocaine) was so widespread in the Andean foothills during the 1980s and 1990s that Peruvian river flood cycles were altered in some areas, making the high-water season unpredictable. The most serious environmental concern (other than deforestation) stemming from the cultivation of coca is the dumping of chemicals (including kerosene, sulfuric acid, acetone, and carbide) used to process coca leaves. However, stopping coca cultivation is nearly impossible due to simple economics: no crop outperforms coca. The CIA claims that some 600,000 hectares of forest are cleared annually for coca and opium poppy cultivation.

Soybean cultivation in South America. Map showing soybean distribution area in South America as of the year 2000. Rainforest and savanna ("cerrado") ecosystems in the Amazon are giving way to soya fields. Images courtesy of the Global Land Use Database at the University of Wisconsin.

In some parts of the world, large-scale commercial agriculture takes up the majority of the productive floodplain and volcanic soils, while leaving smaller farmers little choice but to cut farmland from the rainforest. The ownership of these large commercial farms is concentrated in the hands of a wealthy minority, who may benefit from tax incentives to leave some of their land fallow and not fully employed at any given time. These large farm businesses generally do not employ large numbers of locals, though when they do, workers are used seasonally for low wages. In recent years, grain production in Brazil and other Latin American countries has widely accelerated. However, most of the money ends up in the hands of a few large landowners who, in more marginal areas, have relied on subsidies to survive the harsh soil and climate conditions. Only through these handouts have these landowners been able to turn a profit.

Soybeans have become one of the Brazil's most important crops in the Amazon, as well as in the nearby cerrado grassland ecosystem. Today soybeans are flourishing—since 1998, Brazil has added 30 million acres of soybeans, and American firms are aggressively expanding their presence in the Brazilian agricultural sector. Brazil will likely soon supplant the United States as the world's leading exporter of soybeans, at the expense of the forests of the Amazon basin.

More on soybeans in the Amazon
Paving of road brings change in the Amazon rainforest
Chinese demand drives road-building and deforestation in the Amazon
Brazil's grasslands could replace food production of American heartland

Sustainable Agriculture in the Rainforest

Review questions:

How does large-scale agriculture damage the rainforest?
Why are soybeans generally bad for the Amazon?

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