Tropical rainforests are biologically dense ecosystems with countless plants and animals that thrive together in a delicate cycle. They are important resources for medicines, nutrients and a variety of other purposes. Although located across the globe on several continents, tropical rainforests are considered endangered because of pressures from agriculture, climate change and other forces.
As their name suggests, tropical rainforests are located in the tropics near the equator. About 57 percent of the world's rainforests are located in South America. Brazil holds about a third of the world's rainforests alone. Southeast Asia and various Pacific Islands contain about 25 percent, and West Africa has about 18 percent of the world's total tropical rainforest acreage. Tropical rainforests take up about 6 to 7 percent of the Earth's surface.
With their location near the equator, tropical rainforests are warm with temperatures hovering around 75 to 88 degrees all year. Rainfall is high, and rainforests receive about 80 to 400 inches of rain on average each year. Broadleaf trees are prevalent in rainforests, and because of the consistent temperature, trees don't seasonally lose their leaves.
Although seemingly chaotic with tangles of dense foliage, tropical rainforests have four distinct zones or layers.
The emergent layer is made up of branches from the tallest trees, growing up to 100 to 240 feet. This layer receives the most sun and wind, which makes it warmer than any of the other layers.
The canopy is located beneath the emergent layer. Found about 60 to 90 feet about the forest floor, this layer is where most of the plant and animal life exists. Trees' seeds, fruit and leaves are produced here, which makes it a good zone for food.
The understory is the third layer. Less light reaches this zone, but it is more humid here. Young trees trying to reach through the canopy to receive sunlight dominate this area.
The forest floor is a dark, cool and humid area along the surface of the rainforest. Less than 3 percent of available sunlight reaches this layer. The forest floor, however, has a rich--albeit thin--layer of decomposed material, which keeps nutrients flowing to the rainforest trees.
There is a huge variety of plant life in the tropical rainforest, and up to 80 different species of plants might live in a single acre. To survive in the warm, humid environment of the tropical rainforest, rainforest plants and trees have developed special adaptations. Trees tend to have smooth, thin bark, which prevents other plants from climbing on this surface. Plant leaves generally have tips to allow water to quickly roll off the surface. This prevents mold and bacteria growing from stagnant water. Since some plants, especially trees, must grow to extreme heights to reach sunlight, the root systems of plants in the tropical rainforest generally form to provide support for the plant. Some are wide to form a strong surface. Others form buttresses, which can be up to 30 feet high, and give support to the tree.
A large variety of animals are found in tropical rainforests with as many as 100 different species living in a two-acre zone. Mammals, reptiles, amphibians, and insects thrive in the lush environment where food is plentiful. Like their plant counterparts, the animals of the tropical rainforest have adapted for the unique ecosystem. Some, like primates, use tails and limbs in order to live in the trees. Birds are brightly colored and have special vocalizations. Amphibians--chameleons and geckos--blend into their surroundings.
Tropical rainforests are a delicate ecosystem where all life is interdependent. Trees grow tall to absorb energy from the sun and grow seeds and fruit, which become food for herbivorous animals. These animals are a food source for animal predators. Eventually, the plants and animals will die, becoming food for bacteria, fungus and insects that provide the trees with nutrients. Studies have found that most of the nutrients in the rainforest never make it into the soil, but instead stay in root mats. This makes the soil fairly infertile if the trees are cut down for agriculture or mining areas.
Rainforests are home to about half of the world's plant and animal species, and new varieties are being discovered all the time. A lot of medicines--an estimated 25 percent--are derived from tropical rainforest plants, including aspirin, the anesthetic curane, malaria-treating quinine, and leukemia-fighting rosy periwinkle. Beyond that, it's thought that some 1,400 tropical plants might be used for treatment, even cures, for other forms of cancer. Even without their medicinal uses, the tropical rainforest's plants provide about 40 percent of the Earth's oxygen.