CRISIS IN THE RAIN FOREST
(Page 2 of 6)
July/August 1987
By David Schoonmaker
Even more impressive than the raw totals is the geographical diversity. Imagine 12,500 different types of beetles on 2½ acres in Panama. In Brazil, botanist Ghillean Prance has identified 236 species of trees greater than two inches in diameter in a similar area. In a typical New England woods, you might find five or six species. Ten square feet of rain-forest floor leaf litter has turned up 50 types of ants.
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Two-thirds of the species and as much as 80% of the nutrients in the rain forest are in the canopy. Trees, for example, efficiently and rapidly cycle nutrients and water from the leaf litter into their biomass. Root fungi called mycorrhizae dramatically enhance this process. Because they are so old and receive so little of the nutrients from above, rainforest soils are typically infertile and acidic. They offer little more than a physical base for the rich ecosystem operating dozens of feet above.
The life-forms of this cornucopia have coevolved in ways that drive biologists to dizzy rapture. The ant acacia tree, for example, is completely dependent on its ant residents for defense against other insects and plants. The workers fight off intruders, clean leaves and kill anything that grows within 30 inches of the acacia. In return, the acacia supplies the ants with their entire diet. A successful ant acacia will have fewer than 2% of its shoots occupied by insects other than its ant friends. One without a colony will do poorly, if it survives at all.
An area the size of West Virginia is cleared every year. Thirty busloads of people migrate down the Trans-amazon highway every day.
RAIN FOREST
Imagine 12,500 different species of beetles in 2-1/2 acres.
The rain forest's abundance and complexity have evolved many species that live only in very restricted areas. Of Ecuador's 20,000 different plants, a fifth are endemic. Isolation can make endemism more extreme. Ninety-eight percent of Hawaii's species live nowhere else. Likewise, their density may be very low—perhaps only one individual per acre. Symbiosis, complexity, endemism and rarity all contribute to make the tropical rain forest a fragile ecosystem.
Trees Working
A plethora of products come to us from tropical rain forests. Among the obvious are timber (half the world's annual hardwood harvest), raw materials for latex, Brazil nuts ($16 million worth to the U.S. each year), fruits, oils, spices and even shade-loving houseplants such as the philodendron.
Less well known is the fact that about 25% of all prescription pharmaceuticals are derived from plants growing in tropical rain forests. Alkaloidal drugs from rosy periwinkle found on Madagascar have revolutionized the treatment of lymphocytic leukemia in children. Scientists at the National Cancer Institute state that 70% of the anticancer drugs with promise come from the tropical rain forest. Without curare, heart surgery would be impossible. The medicinal potential in tropical rain-forest plants has barely been touched. Only one in 10 has been examined for medicinal use.
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