| Viewed from the air, a tropical rainforest looks like a large rumpled blanket of foliage. The crowns, or tops, of the trees form a thick canopy, the layer in which most insects and other animals live. In rainforests, canopy trees may rise 50 to 150 feet (15 to 45 meters) before forming a dense celing of branches and leaves. Less than 2 percent of the sunlight filters down through the canopy. The lack of light limits plant growth in the lowest layers of a rainforest. In the warm, damp climate of the tropical rainforest, decomposition on the bottom layer, the forest floor, occurs rapidly. Insects, earthworms, and fungi help decompose plant and animal remains. Nutrients released during decomposition are quickly absorbed by trees and other plants, often leaving the floor relatively bare. Frequent rains leach, or wash away, minerals from the nutrient-poor soil. Millions of animal and plant species live in tropical rainforest, and the discovery of new species continues. Some species can be found only in a tropical rainforest. The okapi, a relative of the giraffe, is one example. More than a thousand kinds of trees have been identified in a square kilometer of tropical rainforest. The rainforest in the South America country of Ecuador has 20,000 kinds of flowering plants. The state of California, a third larger than Ecuador, has only 5,000. Tropical rainforests are a valuable natural resource. Millions of people live in the rainforests, relying on them to fulfill their needs for food and fuel. The rest off the world relies on rainforest for such products as rubber, wood, dyes, oils, foods, and medicines. More than 40 percent of prescription drugs in the United States contain ingredients derived from plants, many of them from rainforests. Rainforests play a role in recycling the earth`s water. Much of the moisture absorbed by the trees transpires from the leaves and evaporates into the atmosphere to return as rainfall. The roots of the trees help anchor the soil and slow water runoff. |
