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Eroded, bright-red soils in Betsiboka Estuary, Madagascar. (Photo courtesy of NASA/JSC)
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EROSION AND ITS EFFECTS
The loss of trees, which anchor the soil with their roots, causes widespread erosion throughout the tropics. Only
a minority of areas have good soils, which after clearing are quickly washed away by the heavy rains. Thus crop
yields decline and the people must spend income to import foreign fertilizers or clear additional forest. Costa
Rica loses about 860 million tons of valuable topsoil every year, while the Great Red Island, Madagascar, loses
so much soil to erosion (400 tons/ha) that its rivers run blood-red, staining the surrounding Indian Ocean. Astronauts
have remarked that it looks like Madagascar is bleeding to death, an apt description of a country with grave environmental
degradation and an ever-declining agricultural economy that depends on its soils. The rate of increase for soil
loss after forest clearing is astonishing; a study in Ivory Coast (Cote d'Ivoire) found that forested slope areas lost 0.03 tons
of soil per year per hectare; cultivated slopes annually lost 90 tons per hectare, while bare slopes lost 138 tons
per hectare.
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Plane view of deforestation-induced erosion in Madagascar
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After heavy tropical rains fall on cleared forest lands, the run-off carries soil into local creeks and rivers.
The rivers carry the eroded soils downstream, causing significant problems. Hydroelectric projects and irrigation
infrastructure lose productivity from siltation, while industrial installations suspend operations due to lack
of water. Siltation also raises river beds, increasing the severity of floods, and creates shoals and sandbars
that make river navigation far more troublesome. The increased sediment load of rivers smothers fish eggs, causing
lower hatch rates. As the suspended particles reach the ocean, the water becomes cloudy, causing regional declines in coral
reefs, and affecting coastal fisheries. The loss of coral reefs worldwide, often labeled the rainforests of the sea, is especially
distressing to scientists because of their tremendous diversity and the important services they provide. Coastal
fisheries are affected not just by the loss of coral reefs and their communities, but by the damage inflicted on
mangrove forests by heavy siltation.
Besides damaging the fisheries industry, deforestation-induced erosion destroys infrastructure of roads and highways
that cross through the forest. The government does not shut down the roads, but must rebuild them repeatedly, using
money that could be used more productively elsewhere.
Erosion is extremely costly for developing countries. Besides the damage to infrastructure, fisheries, and
property, erosion of precious topsoils costs tens of billions of dollars worldwide each year. For example, in the
late 1980s the Indonesian island of Java was losing 770 million metric tons of topsoil every year at an estimated
cost of 1.5 million tons of rice, enough to fulfill the needs of 11.5-15 million people.
ENVIRONMENTAL REFUGEES
Environmental deterioration can leave people as "environmental refugees"—people who are displaced due to environmental degradation. The United Nations says that as many as 50 million people could be considered environmental refugees by 2010 due to deforestation, sea-level rise, expanding deserts, and catastrophic weather events. Red Cross research shows more people are now displaced by environmental disasters than by war.
Review questions:
- Why do rainforests help prevent erosion?
- Why is erosion a problem?
- What are environmental refugees?
[print version | spanish | french | chinese | japanese]
Continued: Species Loss, Extinction and Disease
Unless otherwise specified, this article was written by Rhett A. Butler [Bibliographic citation for this page]
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