A rain forest is a moist, densely wooded area usually found in a warm, tropical wet climate. Annual rainfall is about 80 inches (200 centimeters) and ranges as high as 400 inches (1,000 centimeters) in some tropical rain forests. The average temperature in most rain forests is 80°F (27°C). Broadleaf evergreen trees, vines, sparse undergrowth, and nutrient-poor soils are common characteristics of this kind of forest.
Tropical rain forests encircle the planet, forming an uneven green belt between the Tropic of Cancer and the Tropic of Capricorn. These rain forests are home to nearly half the earth's plant and animal species.
Tropical rain forests once covered more than 4 billion acres (1.6 billion hectares) of the earth. Today, nearly half the tropical rain forests are gone. They now cover only about 7 percent of the earth's land, including parts of South and Central America, central Africa, and Southeast Asia. The largest continuous rain forest lies in South America, where about 2.7 million square miles (6.9 million square kilometers) of forest cloak the Amazon Basin.
Though fewer in number than in the tropics, rain forests grow in temperate regions as well. Temperate rain forests have a more seasonal climate, with less constant temperatures and less rain, than do rain forests near the Equator. Though plant and animal life are abundant, the species are not as diverse as they are in warmer, tropical rain forests.
Layers of Life
Viewed from the air, a tropical rain forest looks like a 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 rain forests, canopy trees may rise 50 to 150 feet (15 to 45 meters) before forming a dense ceiling 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 rain forest. In the warm, damp climate of the tropical rain forest, 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 rain forests, and the discovery of new species continues. Some species can be found only in a tropical rain forest. 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 rain forest. The rain forest in the South American country of Ecuador has 20,000 kinds of flowering plants.
The state of California, a third larger than Ecuador, has only 5,000.
Tropical rain forests are a valuable natural resource. Millions of people live in rain forests, relying on them to fulfill their needs for food and fuel. The rest of the world relies on rain forests 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 rain forests.
Rain forests 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.
Vanishing Rain Forests
Clearing forestlands for farming, ranching, logging, and mining is rapidly decreasing the remaining rain forests. Some scientists estimate that an area of tropical rain forest the size of the U.S. state of Delaware is cleared every month.
Although the land is often used for agriculture, the nutrient-poor tropical soils can support crops or cattle for only a few years. Then the land is abandoned, and people move elsewhere in the forest. Erosion accelerates as the cleared land is exposed to torrential rains and blistering sunlight.
The destruction is no longer going unnoticed. Governments, scientific organizations, conservationists, and other citizens are deeply concerned about the loss of rain forests. They also recognize that people need the food and fuel that forests provide.
The future of the earth's rain forests may depend on management plans that preserve some areas of rain forest while allowing people to cut trees selectively in other areas.
Better land-use practices, education, and wiser planning may slow deforestation, but experts worry that the rain forest will be virtually gone by the time these changes can be widely implemented.
Return to Combustion in the RainForest
This article is adapted from the book "Exploring Your World: The Adventure of Geography", from the National Geographic Society.
Copyright ©1996 Business to Business Magazine Inc.