CRISIS IN THE RAIN FOREST
(Page 3 of 6)
July/August 1987
By David Schoonmaker
Rain forests are also potent climatic and environmental stabilizers. At least 50%, and in some cases as much as 80%, of the rain that falls on them is evaporated or transpired by plants back into the air—cleansed—within a week. A fifth of the earth's fresh water cycles through the Amazonian filter and back to the Atlantic each year. On the order of 200 billion tons of carbon is bound up in the plants of the rain forest, carbon that might otherwise be in the form of carbon dioxide and contribute to the greenhouse effect.
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Devastation
As few as 3,000 years ago, tropical rain forests covered more than 3 million square miles of Earth's surface—twice what they do now. They are currently being converted to nonproductive forest and agricultural lands at a rate of about 25,000 square miles, an area about the size of West Virginia, each year. Two-thirds of the rain forest in Central America is already gone. Madagascar and the Ivory Coast will be completely stripped by 2000—sooner if cutting rates increase. Worldwide, 20% of the present rain forest will be gone by 2000. Even these ominous figures may be optimistic, since deforestation rates are increasing nearly everywhere and in some places (Brazil's Rondonia and Acre states, for example) at exponential rates.
Even the selective cutting of trees won't serve as an effective preservative. Beyond a threshold level of thinning—about 30% removal of the canopy—rain forest ceases to be rain forest. Sunlight dries the forest floor, disrupting the fragile system. The effect on animals may be even more profound. A loss of 10% of habitat can result in a 50% loss of species. In some areas, over 90% of the birds are so accustomed to the relative darkness of the rain forest that they won't cross a clearing to breed or to find food.
Rain forests don't regenerate quickly, either. As long as the logged area isn't burned (as most are) and isn't too large, vegetation may approach the original state in 50 to 120 years. In massive slash-and-burn operations, however, the rain forest may never return to full verdancy. Endemic species may be entirely lost, or the cut may be too big to reseed naturally. After all, it isn't surprising that something that took eons to reach its present state won't regenerate within decades.
Cutting large areas of rain forest also may affect regional climate enough to harm untouched rain forest (not to mention area agriculture). Because a rain forest returns so much rain to the atmosphere, moisture is recycled many times before it finally flows back to the ocean. But when the trees are removed, rain runs off at as much as 20 times the rate as before. Water flowing away down silt-laden rivers will be unavailable for trees downwind. If, as is now feared, 8% of Brazil's tropical rain forest is cut by 2000, average rainfall in the Amazon may drop by 25 inches annually.
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