Other Environmental Themes

Erosion Control

Trees and other vegetation stabilize landscapes, holding soils in place and helping them retain moisture. Plants also protect soils from erosion by shielding them from the full impact of raindrops. In addition, plants can act as a giant pump, siphoning water with their roots and releasing it to the atmosphere through a process called evapotranspiration.

These services, though tremendously valuable, are inconspicuous to the casual glance and only become noticeable when landscapes become denuded by deforestation, agricultural clearing and other land-use practices. Rain quickly turns soils into mud, which inhibits the infiltration of water, thereby increasing runoff and enhancing the odds of subsequent flood damage. Dislodged soil particles are swept downstream by the rushing water, turning rivers into muddy channels, clogging dams, degrading water supplies and suffocating coastal zones in a blanket of silt that can severely harm offshore fisheries and coral reefs.

The costs of erosion are considerable; each year, the hydroelectric capacity lost worldwide as reservoirs fill with silt has been estimated at $6 billion. More substantial losses are incurred through flood damage, water contamination and impaired fisheries. However, the toll in human suffering and devastation can be far greater still.

In 1998, Hurricane Mitch unleashed one of the worst disasters in Central American history. The storm dumped 50 inches of rain on parts of Honduras and Nicaragua that had been stripped of vegetation through deforestation and drought. The ensuing mudslides and floods killed more than 10,000 people and forced more than a million others from their homes. Disaster struck again in 1999: An estimated 30,000 people lost their lives in Venezuela after heavy rains left slum dwellings-many of which had been built on barren, overdeveloped hillsides-submerged beneath water and mud.

A decade earlier, mudslides buried villages in southern Thailand, killing several hundred people. The nation's prime minister blamed the disaster on loggers who had cleared forests that would have otherwise helped restrain the floodwaters. A few months after the tragedy, the prime minister persuaded the cabinet to ban clearcutting throughout the country. If enforced over the long term, measures like this might prevent similar calamities from occurring in the future-in Thailand, as well as in other nations-assuming deforestation is not already too extensive.