Rain Forest

Tropical rain forests are large areas that are warm and wet throughout the year, and whose tall evergreen trees are so dense they form a canopy. As the richest ecosystem (an area in which living things interact with each other and the environment) on Earth, rain forests support such a diversity of life that at least half of all the world's species of plants and animals live there. Rain forests also play a role in the world's climate, and are among the most fragile ecosystems.

Most rain forests are located in the central region of Earth, near the equator, where temperatures typically range between 73° and 87°F (22.78°C and 30.56°C). Most receive some rain almost every day, averaging more than 100 inches (254 centimeters) a year, and sometimes twice that much. This rain is soaked up from the soil by the lush plants and enormous trees that then return it to the air via transpiration. Transpiration occurs in all plants as they naturally lose water vapor through their leaves.

At least half of this water released by plants falls back down again onto the rain forest as rain. Since all tropical rain forests lie near the equator, daylight lasts 12 hours throughout the year, and the steady warmth of

the land heats the air above it, causing it to rise and release its moisture (rain). Everything growing below is always green and flowers regularly.

LAYERS OF A RAIN FOREST

The largest rain forest is the Amazon in South America, and it is typical of what is called a tropical rain forest, as opposed to a temperate rain forest which is located in a cooler climate. A tropical rain forest like the Amazon is a complex system that can be divided into different horizontal layers (like floors in an apartment building). As with an apartment building, there are different things going on at different levels.

Forming the topmost layer are the tallest of the rain forest's trees. Able to sometimes grow as high as a football field is long, these giants are scattered throughout the forest. The next level or layer is called the canopy, because it shades everything below. This green roof is created by a dense thicket of trees that stand between 60 and 150 feet (18.29 and 45.72 meters) high and whose branches and leaves are so close together that they form an umbrella over the rest of the forest below. These trees grow so tightly that rainfall reaches the ground only by running down the tree trunks or the stems of other plants. The canopy is alive with animal life as well, such as iguanas, tree frogs, monkeys, and bats.

The next section is called the understory and includes smaller trees, ferns, vines and palms, and smaller bushes. Since the canopy traps and holds much of the heat and moisture, the understory is extremely hot and humid. It also does not have many flowering plants because of the lack of direct sunlight. The bottom level, or the forest floor, is covered with shade-loving mosses, herbs, and fungi, as well as dead plants and animals. The forest floor receives only 2 percent of the sunlight needed for photosynthesis (the process by which plants use light energy to make food). Dead material on the forest floor decomposes very quickly, thus providing nutrients to the soil and everything that grows in it. Masses of insects and the animals that feed on them, like the anteater, also live on the forest floor. Many of these animals, like bats, mice and rats, and porcupines, are nocturnal or active only at night. Some, like monkeys and apes, are busy during the day, while still others, like large cats and wild dogs, are most active at dusk and dawn.

PLANT LIFE IN THE RAIN FOREST

No other biome (a particular type of large geographic region) on Earth can match the tropical rain forest for its diversity of plant and animal species. All of these species, however, have the same thing in common. As rain forest dwellers, they all have adapted in many ways to life in this special ecosystem. One example of plant adaptation is a tree's buttresses or "prop roots" that spread out above ground and help support the tree in the shallow, unstable soil of the forest floor. Other trees often grow stilt roots or "air roots" which grow out from its trunk as high up as 10 to 12 feet (3.0 to 3.66 meters) and help spread the weight of the tree over a wider area.

Leaf structure is also highly adapted. Some leaves have what are called "drip tips"—a special shape that helps rainwater and condensation run off easily. This allows the leaf to breathe better. Other plants called epiphytes grow on or in trees and never actually touch the soil.

ANIMAL LIFE IN THE RAIN FOREST

Animal life in the rain forest is equally adapted and strange and fascinating. The vast majority of all species are insects, although there are twice as many mammals and birds in its tropical environment as there are in temperate zones. South America is especially rich in birds, bats, and fishes. Rain forest species often have spectacular shapes, colors, or sizes. These include the huge-billed toucan, the brilliantly colored American butterfly with a wingspan of nearly 8 inches (20.32 centimeters), the huge, scary-looking fruit bat, the goliath frog that can weigh as much as 33 pounds (14.98 kilograms), and the bizarre-looking anteater. These are but a few of the thousands of exotic life forms that crawl, slither, hop, fly, and teem about in the tropical rain forest.

CONSEQUENCES OF RAIN FOREST DESTRUCTION

Despite this great diversity and obvious abundance of life, tropical rain forests can be easily and severely damaged, and they take an extremely long time to recover. Their soil is usually ancient and poor in minerals that are mostly bound up in the incredible amounts of vegetation it has to support. Although rain forests are highly productive ecosystems, this productivity is based on the constant sunlight and steady rains, and not on rich, thick soil. When trees are cut down and burned in a typical practice called "slash and burn," the landscape suffers severely. This is usually done to clear the land for farming and roadbuilding. Logging also clears large areas. When this occurs, the thin soil is exposed and the steady rains wash it away, leaving behind "wet deserts" and causing devastating floods. An area twice the size of Maine is cleared this way every year, and with it often go the unique plants and animals it supported.

Rain forest destruction means not only plant and animal extinction because of habitat loss but possibly an increase in the "greenhouse effect" as fewer trees exist to absorb the increasing amounts of carbon dioxide people produce. This causes Earth's atmosphere to trap too much heat and could lead to global warming.

[See alsoBiodivesity; Biome; Forest ]