Definition
Rainforests are forests characterized by high rainfall, with definitions setting minimum normal annual rainfall between 1750–2000 mm (68-78 inches).
Basics
A rainforest (or rain forest) is a tropical forest that gets a lot of rain. It usually has a lot of plants and animals. A very well known rainforest is the Amazon Rainforest. Most of it is in Brazil, though Ecuador, Colombia, Chile and other countries have parts of it.
Scientists say over half of all plant and animal species live in the rainforest. Also more than 1/4 of all medicines come from here. Covering only 2% of the Earth's land area they still provide 40% of the oxygen.
The rainforest can be found in three major geographical areas around the world.
- Central America in the Amazon River basin.
- Africa - Zaire basin, with a small area in West Africa; also eastern Madagascar.
- Indo-Malaysia - west coast of India, Assam, Southeast Asia, New Guinea, and Queensland, Australia.
The rainforest gets an average of 50 to 250 inches of rain a year. It is warm year round rarely getting above 93 F or getting below 68 F. It has an average humidity of 77 to 88% The rainforest has carpet of green rot leaves on the floor. This is called the humus layer. Rainforests are in danger of deforestation because lumber industries are chopping down the trees for profit.
The three layers
Most scientists think of the rainforest in three layers. The top layer is the canopy. The canopy is the tallest trees that grow to be 75-150 feet tall. Under the tall canopy is the understory. The understory is made up of smaller trees, vines, and shrubs. The bottom layer is the forest floor. This is made up of the small plants on the ground.
The canopy is like a huge green roof over the forest. The trees grow up thin and straight, like pillars. They do not put out branches until they are very tall. Then, they spread out like an umbrella in the sunlight. The trees are so close together that very little light or rain goes through to the lower layers. Many kinds of monkeys, birds, and insects live in the canopy. These kinds of animals often never touch the ground in their entire life. All the food and water they need, they find among the tall trees. Because it rains all the time, water can be found in holes in the trees, leaves, and plants that grow on the trees. The animals eat the leaves and fruit of the trees, insects, or other animals. The tall canopy trees must be able to reach the sunlight high in the air and still get nutrients from the thin soil on the forest floor. Their roots do not go deep into the soil because there is nothing there for the plants to reach. Instead the roots spread out in all directions along or just under the ground. That way they can quickly make use of the nutrients from the recycled plants and animals that have fallen to the floor.
The understory is usually a dark, humid place. There is very little light and no breeze because they are blocked out by the canopy. The plants under the canopy must be able to live with very little sunlight. Often they will only grow in open patches where a big tree has fallen down. Other plants, like vines, grow on the big trees. They get the nutrients they need from the tree, which is getting sunlight up in the canopy.
The floor of the rain forest is often very open and easy to walk across. That is because so little light reaches the floor that very few plants can grow there. Most people think wrongly because of most movies, that show people cutting their way through the thick plants and vines in the jungle. That type of jungle is only found around rivers and clearings, where light can reach the forest floor.
Plants and animals
One type of plant in the rain forest does not even need soil. These plants are called epiphytes, or air plants. Air plants ilve on the branches of other trees in the canopy or understory, with their roots out in the air. In the humid rainforest, they collect water from the rain that falls on them.
One kind of air plant is a flower called an orchid. There are thousands of different kinds of orchids in the rain forest! Some air plants store water in pools in and around their roots. These pools can become homes for frogs and salamanders. Frogs usually need to lay their eggs in ponds, but some rain forest tree frogs lay their eggs in the pools in air plants. That way the frogs never have to go down to the ground.
Millions of kinds of insects live in the rain forest. It never gets cold enough to kill them. There are bees, butterflies, termites, beetles, and many kinds of flies. There are ants everywhere. One of the more interesting kinds of ants is the army ant. Army ants do not have nests. They march out in a line every day to hunt for other insects, which they eat. At night they hook themselves together to form a living nest around their queen and larvae, or baby ants.
Snakes live in the trees and on the forest floor. They eat frogs, eggs, birds, insects, and small animals. Some of the snakes, like the fer-delance of Latin America, are poisonous, but others are not. One especially large non-poisonous snake is the anaconda of South America. It is one of the largest snakes in the world. A full-grown anacoda kills its prey by wrapping itself around the animal and squeezing it until it cannot breathe. Then the snake swallows the prey whole. If the animal is big enough, the snake may not eat again for weeks.
Monkeys are a very common animal in the rain forest. Most live their lives up in the canopy and the understory. They have long arms to swing from branch to branch, and some use their tails to hold onto the trees while they eat. They are very fast and agile, jumping easily from tree to tree for food. Different monkeys eat different things. They can eat nuts, flowers, roots, and frogs. Their hoots and howls are heard throughout the rainforest, even when they cannot be seen among the trees.
Many colorful birds also live among the canopy of the rain forest, and there are also animals that live on the forest floor. The tapir is a forest animal that looks like a large pig. It is actually in the same animal family as the horse and the rhinoceros. They live in South American and Asian rain forests, eating leaves, twigs, and fruit. Tapirs are the only one of the animals hunted by the big cats of the rain forest. Jaguars, leopards, and tigers are the largest predators of the rain forest. All of these cats have beautiful fur coats that have made them desired by hunters for years. The spotted coats of the jaguar and leopards were especially popular for fur coats. Today most countries are trying to protect their big cats, but many are still hunted illegally.
These are only a few of the animals and plants in the rain forest, because the rain forest is where the plants and animals are the most abundant. About half of all of the different kinds, or species, of plants and animals in the entire world live in rain forests. Many of the plants, animals, and insects do not even have names, because they have never been classified by a scientist.
Amazon Rainforest
The Amazon Rainforest is the forest that grows in the tropical basin of the Amazon River.
The forest lies in a basin drained largely by the Amazon River, with 1100 tributaries. This basin was formed in the Paleozoic period, between 500 and 200 million years ago.
Biodiversity: Wet tropical forests are the most species-rich biome, and tropical forests in the Americas are consistently more species rich than are African and Asian wet forests. As the largest tract of tropical rainforest in the Americas, Amazonian rainforests have unparalleled biodiversity
The region is home to ~2.5 million insect species, tens of thousands of plants, and some 2000 birds and mammals. The diversity of plant species is the highest on earth with some experts estimating that one square kilometre may contain over 75,000 types of trees and 150,000 species of higher plants. One square kilometre of Amazon rainforest can contain about 90,000 tons of living plants. This constitutes the largest collection of living plants and animal species in the world. One in five of all the birds in the world live in the rainforests of the Amazon. To date, an estimated 438,000 species of plants of economic and social interest have been registered in the region with many more remaining to be discovered or cataloged. (Note: Brazil has one of the most advanced laws to avoid biopiracy, but enforcing it is a problem.)
Amazonian forests as a store of carbon dioxide: More than one fifth of the Amazon Rainforest has already been destroyed. The forest which remains is threatened. People who care for the envirnoment warn about the loss of biodiversity. They also point out that releasing the carbon which is stored in the trees will increase global warming.
About 10% of the world's carbon is stored in the Amazonian forest. — on the order of 1.1 x 1011 metric tonnes of carbon. Amazonian forests are estimated to have accumulated 0.62 ± 0.37 tonnes of carbon per hectare per year between 1975 and 1996. Fires related to Amazonian deforestation have made Brazil one of the biggest greenhouse gas producers. Brazil produces about 300 million metric tonnes of carbon dioxide a year; 200 tons of these are from logging in the pubes(pdf file). In 1996, the Amazon was reported to have a 34 per cent increase in deforestation since 1992. A new report by a congressional committee says the Amazon is vanishing at a rate of 52,000 square kilometers (20,000 miles²) a year, over three times the rate for which the last official figures were reported, in 1994.
Conservation: Some people have calculated that it may even pay to save the forest. They said that one hectare of Amazonian forest in Peru is worth about US $ 6280, if it is used to harvest fruits, latex and timber (wood). If all the wood is cut down for timber, it has a value of about US $ 1000. Obviously, this can only be done once; it is not sustainable. When the forest has been cleared, the hectar of land can be used as a pasture, and is worth about US $ 148. Not all people agree on the study; some have questioned the assumptions behind it.
The Força Aérea Brasileira has been using EMBRAER R-99 surveillance aircraft to monitor the forest. This was done as part of the SIVAM program. At a conference in July 2004, scientists warned that the rainforest will no longer be able to absorb the millions of tons of greenhouse gases annually, as it usually does, because of the increased speed of rainforest destruction.
9,169 square miles of rain forest were cut down in 2003 alone. In Brazil alone, European colonists have destroyed more than 90 indigenous tribes since the 1900's. With them have gone centuries of knowledge of the medicinal value of rainforest species. As their homelands continue to be destroyed by deforestation, rainforest peoples are also disappearing.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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