Rainforest | Research & Encyclopedia Articles

Rainforest

Rainforests receive more than 200 days of rain per year, or as much as 240 inches of water. They are characterized by thousands and even millions of plants and trees growing thickly over the land, which soak up rainwater from the soil and return it to the air through transpiration. At least half of that water then falls back down onto the forest as rain again. Most rainforests are located in the central region of the earth, near the equator, where temperatures range from 70 to 90 degrees Fahrenheit or warmer. At least fifty percent of the northern half of South America is covered in rainforest, as is most of Central America, the middle portion of Africa and southern Asia, and even small parts of northern Australia. Together, rainforests cover approximately seven percent of the earth's land surface.

Some rainforests are believed to have existed for 100 million years. At least half of all of the world's species of plants and animals make rainforests their habitat. For example, the largest rainforest, the Amazon in South America, has at least 1,600 species of birds alone, and approximately one million types of insects. The Amazon occupies approximately 2.5 million square miles, or two-thirds the size of the United States, and makes up half of the world's remaining rainforest. Many of the plants found in the rainforest have been found to have medicinal value, accounting for more than one-fourth of all medicines. The diversity of life in a rainforest makes it a truly unique habitat compared with the rest of the world, where only five percent of this diversity is likely to exist.

These complex ecosystems are vital to the world's climate, because of the large amount of rainfall transpired by the plants within them. While some of the rain falls back into the rainforest, the rest travels with warm currents of air to cooler sections of the earth to the north and south. The plants also absorb carbon dioxide (CO₂) from the atmosphere, and return vast amounts of oxygen (O₂) for other species to breathe.

A rainforest can be divided into horizontal layers according to the plants and animals living in them. The top layer includes the tallest trees that scatter themselves throughout the forest, called the emergents. They can grow to be 300 feet (914 meters) tall and extend themselves above the next layer of forest growth, called the canopy. This most productive area of the forest includes trees that stand 60 to 150 feet (183 to 457 meters) high, with branches and leaves that form an umbrella over the underlying forest. These trees grow so tightly together that rainfall reaches the ground only by running down the tree trunks or the stems of other plants. The canopy is alive with flower and animal life as well, such as iguanas, tree frogs, monkeys and bats, and countless birds and insects. The next section, called the understory, includes smaller trees, ferns, vines and palms, and smaller bushes. Because the upper canopy traps much of the heat and moisture into the forest, the understory is extremely hot and humid with few flowering plants due to the lack of sunlight. The bottom layer, the forest floor, is filled with shade-loving mosses, herbs and fungi, and dead plants and animals. These decompose quickly, providing nutrients through the soil to the larger plants above. Thousands of insects and larger animals that feed on them, such as the anteater, live on the forest floor.

There are three primary types of rainforests: tropical, mangrove, and temperate. Tropical forests include those found closest to the equator, and are the wettest regions of the world. Some have wet and dry seasons, and others are found at the top of tropical mountains where clouds surround the mountain peaks most of the time. Mangrove rainforests grow along the oceans and soak up ocean and rainwater. Temperate rainforests exist in cooler climates along the western coast of North and South America, and in southern Australia and New Zealand. They include many of the "old-growth" forests such as the sequoia trees in northern California. Some of the sequoias are more than 1,000 years old.

While the rainforests have included people in small tribes for thousands of years, encroaching populations on these regions of the world have placed many rainforests in danger. Approximately 50 million acres (20 million hectares) of rainforests are disappearing each year, or 90 acres (36 hectares) every minute, as trees are harvested, and the land is cleared for farming, animal grazing, or for roads. In most cases, the trees are cut down and burned, a process called "slash and burn," which produces tons of smoke and CO₂ gases. As fewer trees exist to absorb this CO₂, these warm gases increase and contribute significantly to the greenhouse or warming effect on the earth's atmosphere. Decreased vegetation also causes increased flooding in these areas, and subsequent erosion of vital topsoil. Habitat disappears for various animal and plant species. It is impossible to accurately predict how many species become extinct each year due to the rainforest's destruction. Efforts to stop this destruction include creating reserves or protected regions where limited harvesting of trees or fruits, plants and nuts is allowed.