Rainforests are forests characterized by high rainfall, with definitions setting minimum normal annual rainfall between 1750–2000 mm (68-78 inches). The monsoon trough, alternately known as the intertropical convergence zone, plays a significant role in creating Earth's tropical rain forests.
40 to 75% of all species on the world's habitats are indigenous to the rainforests. It has been estimated that many millions of species of plants, insects, and microorganisms are still undiscovered. Tropical rainforests have been called the "jewels of the Earth", and the "world's largest pharmacy", because over one quarter of natural medicines have been discovered there. Rainforests are also responsible for 28% of the world's oxygen turn over, often misunderstood as oxygen production, processing it through photosynthesis from carbon dioxide and storing it as carbon through biosequestration.
The undergrowth in a rainforest is restricted in many areas by the lack of sunlight at ground level. This makes it possible to walk through the forest. If the leaf canopy is destroyed or thinned, the ground beneath is soon colonized by a dense, tangled growth of vines, shrubs, and small trees called a jungle. There are two types of rainforest, tropical rainforest and temperate rainforest.
Many of the world's rainforests are associated with the location of the monsoon trough, also known as the intertropical convergence zone. Tropical rainforests are rainforests in the tropics, found near the Equator (between the Tropic of Cancer and Tropic of Capricorn) and present in Southeast Asia (Myanmar to Philippines, Indonesia, Papua New Guinea, and northeastern Australia),Sri Lanka, Sub-Saharan Africa from Cameroon to the Congo (Congo Rainforest), South America (e.g. the Amazon Rainforest), Central America (e.g. Bosawás, southern Yucatán Peninsula-El Peten-Belize-Calakmul), and on many of the Pacific Islands (such as Hawaiʻi). Tropical rainforests have been called the "Earth's lungs," although it is now known that rainforests contribute little net oxygen additions to the atmosphere through photosynthesis.
Temperate rainforests are rainforests in temperate regions. They can be found in North America (in the Pacific Northwest, the British Columbia Coast, and in the inland rainforest of the Rocky Mountain Trench east of Prince George), in Europe (parts of the British Isles such as the coastal areas of Ireland, Scotland, southern Norway, parts of the western Balkans along the Adriatic coast, as well as in the North West of Spain and coastal areas of the eastern Black Sea, including Georgia and coastal Turkey), in East Asia (in southern China, Taiwan, much of Japan and Korea, and on Sakhalin Island and the adjacent Russian Far East coast), in South America (southern Chile) and also Australia and New Zealand.
A tropical rainforest is typically divided into four main layers, each with different plants and animals adapted for life in that particular area: the emergent, canopy, understory, and forest floor layers.
The emergent layer contains a small number of very large trees called emergents, which grow above the general canopy, reaching heights of 45–55 m, although on occasion a few species will grow to 70–80 m tall. They need to be able to withstand the hot temperatures and strong winds in some areas. Eagles, butterflies, bats, and certain monkeys inhabit this layer.
The canopy layer contains the majority of the largest trees, typically 30–45 m tall. The densest areas of biodiversity are found in the forest canopy, a more or less continuous cover of foliage formed by adjacent treetops. The canopy, by some estimates, is home to 50 percent of all plant species, suggesting that perhaps half of all life on Earth could be found there. Epiphytic plants attach to trunks and branches, and obtain water and minerals from rain and debris that collects on the supporting plants. The fauna is similar to that found in the emergent layer, but more diverse. A quarter of all insect species are believed to exist in the rainforest canopy. Scientists have long suspected the richness of the canopy as a habitat, but have only recently developed practical methods of exploring it. As long ago as 1917, naturalist William Beebe declared that "another continent of life remains to be discovered, not upon the Earth, but one to two hundred feet above it, extending over thousands of square miles." True exploration of this habitat only began in the 1980s, when scientists developed methods to reach the canopy, such as firing ropes into the trees using crossbows. Exploration of the canopy is still in its infancy, but other methods include the use of balloons and airships to float above the highest branches and the building of cranes and walkways planted on the forest floor. The science of accessing tropical forest canopy using airships, or similar aerial platforms, is called dendronautics.
The understory layer lies between the canopy and the forest floor. The understory (or understorey) is home to a number of birds, snakes, and lizards, as well as predators such as jaguars, boa constrictors, and leopards. The leaves are much larger at this level. Insect life is also abundant. Many seedlings that will grow to the canopy level are present in the understory. Only about 5 percent of the sunlight shining on the rainforest reaches the understory. This layer can also be called a shrub layer, although the shrub layer may also be considered a separate layer.
The forest floor, the bottom-most layer, receives only 2 percent of sunlight. Only plants adapted to low light can grow in this region. Away from riverbanks, swamps, and clearings where dense undergrowth is found, the forest floor is relatively clear of vegetation because of the low sunlight penetration. It also contains decaying plant and animal matter, which disappears quickly due to the warm, humid conditions promoting rapid decay. Many forms of fungi grow here which help decay the animal and plant waste.
More than half of the world's species of plants and animals are found in the rainforest. Rainforests support a very broad array of fauna including mammals, reptiles, birds, and invertebrates. Mammals may include primates, felids, and other families. Reptiles include snakes, turtles, chameleons, and other families while birds include such families as vangidae and Cuculidae. Dozens of families of invertebrates are found in rainforests. Fungi are also very common in rainforest areas as they can feed on the decomposing remains of plant and animal life. These species are rapidly disappearing due to deforestation, habitat loss, and biochemical releases into the atmosphere.
Despite the growth of vegetation in a tropical rainforest, soil quality is often quite poor. Rapid bacterial decay prevents the accumulation of humus. The concentration of iron and aluminium oxides by the laterization process gives the oxisols a bright red color and sometimes produces minable deposits such as bauxite. Most trees have roots near the surface as there are not many nutrients below the ground; most of the trees minerals come from the top layer of decomposing leaves (mainly) and animals. On younger substrates, especially of volcanic origin, tropical soils may be quite fertile. If the trees are cleared, the rain can get at the exposed soil, washing it away. Eventually streams will form, then rivers. Flooding becomes possible.
A natural rainforest emits and absorbs vast quantities of carbon dioxide. On a global scale, long-term fluxes are approximately in balance, so that an undisturbed rainforest would have a small net impact on atmospheric carbon dioxide levels, though they may have other climatic effects (on cloud formation, for example, by recycling water vapor). No rainforest today can be considered to be undisturbed. Human induced deforestation plays a significant role in causing rainforests to release carbon dioxide, as do natural processes such as drought that result in tree death. Some climate models run with interactive vegetation and predict a large loss of Amazonian rainforest around 2050 due to drought, leading to forest dieback and the subsequent feedback of releasing more carbon dioxide.
Tropical rainforests provide timber as well as animal products such as meat and hides. Rainforests also have value as tourism destinations and for the ecosystem services provided. Many foods originally came from tropical forests, and are still mostly grown on plantations in regions that were formerly primary forest. Also, plant derived medicines are commonly used for fever, fungal infections, burns, gastrointestinal problems, pain, respiratory problems, and wound treatment.
On January 18, 2007, FUNAI reported that it had confirmed the presence of 67 different uncontacted tribes in Brazil, up from 40 in 2005. With this addition, Brazil has now overtaken the island of New Guinea as the country having the largest number of uncontacted tribes. The province of Irian Jaya or West Papua in the island of New Guinea is home to an estimated 44 uncontacted tribal groups.
Central African rainforest is home of the Mbuti pygmies, one of the hunter-gatherer peoples living in equatorial rainforests characterised by their short height (below one and a half metres, or 59 inches, on average). They were the subject of a study by Colin Turnbull, The Forest People, in 1962. Pygmies who live in Southeast Asia are, amongst others, referred to as “Negritos.”
Tropical and temperate rainforests have been subjected to heavy logging and agricultural clearance throughout the 20th century and the area covered by rainforests around the world is shrinking. Biologists have estimated that large numbers of species are being driven to extinction (possibly more than 50,000 a year; at that rate, says E. O. Wilson of Harvard University, a quarter or more of all species on Earth could be exterminated within 50 years) due to the removal of habitat with destruction of the rainforests.
Another factor causing the loss of rainforest is expanding urban areas. Littoral rainforest growing along coastal areas of eastern Australia is now rare due to ribbon development to accommodate the demand for seachange lifestyles.
The forests are being destroyed at a rapid pace. Almost 90% of West Africa's rainforest has been destroyed. Since the arrival of humans 2000 years ago, Madagascar has lost two thirds of its original rainforest. At present rates, tropical rainforests in Indonesia would be logged out in 10 years and Papua New Guinea in 13 to 16 years.
Several countries, notably Brazil, have declared their deforestation a national emergency. Amazon deforestation jumped by 69% in 2008 compared to 2007's twelve months, according to official government data. Deforestation could wipe out or severely damage nearly 60% of the Amazon Rainforest by 2030, says a new report from WWF.
However, a January 30, 2009 New York Times article stated, "By one estimate, for every acre of rain forest cut down each year, more than 50 acres of new forest are growing in the tropics..." The new forest includes secondary forest on former farmland and so-called degraded forest.
From a new recent report in September 2009, new opportunities are beginning to discover they could save the rainforest. In Brazil, Environment Minister Carlos Minc announced proudly that the rate of deforestation of the Amazon fell by 46 percent last year. That means the lowest logging level since the country began to keep annual statistics 21 years ago. But not only Brazil has reduced deforestation as a whole also slowed the loss of forest down. The annual decline is now over two thousand. Deforestation decreases in a country as it becomes richer and more industrialized. Therefore, there are exceptions in a group of countries where deforestation has become so profitable that it is an important part in the growth of prosperity. New goal is to stop felling the forest, but also in managing the forest long-term, which occurs on a larger scale. More police officers guarding the rainforest, and stifle the illegal logging..
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 6% (they used to cover 14% but were destroyed by deforestation) 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.
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.
Most scientists think of the rainforest in four layers. The top layer is the Emergent layer. Then is the canopy layer. The canopy is made of 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 emergent layer is found at the top of the trees. High in the trees eagles perch. Their keen eyes search constantly for small moneys and other prey. Butterflies, parrots, toucans, and hundreds of other colorful birds constantly fly through the tops of the trees.
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, found under the canopy. 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. Bushes, large green plants, and small trees make up this layer. 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 ground level is called the forest floor. Snakes, tapirs, jaguars, tamanduas, and gorillas are just a few of the species that live here. It is dark on the rain forest floor. Insects, giant centipedes, spiders, ants, and beetles are also very abundant here. 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.
One type of plant in the rainforest does not need soil. These plants are called epiphytes, or air plants. Air plants live 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. [[File:|thumb|alt=A graceful orchid|A white orchid]] One kind of air plant is a flower called an orchid. There are thousands of different kinds of orchids in the rainforest. 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 rainforest 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 rainforest. It never gets cold enough to kill them. There are bees, butterflies, termites, beetles, and many kinds of flies. There are ants everywhere. One kind of ant 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 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 rainforest. 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 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 rainforest. 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.
There are many tribes of people who have lived in the rainforests for thousands of years. These forest dwellers usually belong to one of two groups. They are usually hunter/gatherers or slash-and-burn farmers.
Hunter/gatherers live as they do in every other region of the world. They kill animals and gather what the forest provides for part of their food. Unlike in the Artic, tools are always available. Unlike in the desert, water is always available. The people do not need clothes to protect them from the weather. The forest even provides a way to make hunting easier. Many of the people hunt with poisoned arrows. The poisons come from the plants of the forest. That makes the animals easier to kill.
Most of the forest people are slash-and-burn farmers. They raise crops in small clearings as well as hunting and gathering in the forest. This provides them with food year-round. They start by cutting (slashing) down the trees and the other plants in an area. They let the dead plants dry out, then they burn them. The ash from the burned platns goes into the soiil and makes it fertile for a little while. This is called slash-and-burn farming.
The small clearings grow food crops for a few years, then the family or group moves on and clears a new field. The old field is left to be overgrown by the forest. In a few years, it once again looks like the rain forest that surrounds it.
This type of farming does not harm the rain forest when only a few people are doing it. The small clearings become rain forest again without any damage. The land is used and recycled for use again some other time. The rain forest easily regrows to fill in the clearings after the people leave. That is changing today. Today, the rain forests asre getting smaller because too many people are burning them.
There are some serious problems concerning the rainforests that need to be fixed. Rain forests are being cut down too quickly. Every year an area about the size of West Virginia is being destroyed. This is a problem for everyone.
Rain forests are so large and thick that for many years very few people lived or went there. Today, however, that is changing. Millions of poor, often hungry, people live near the rain forests of the world. These people are desperate for a better life, and they think they can find it in the forests.
Settlers can get into the rain forests because modern machines have opened roads deep into the jungle. The roads are usuaslly built by businesses who want to cut down trees or dig up minerals in the forest. Governments build other roads for trade and to allow settlers into the forest. Poor people come into the forest by the thousands on the roads and take land to raise food. They burn off the trees and plants to make a field. Then they plant crops for food and to sell. All around them other farmers do the same, so there is no forest left to grow back.
The new farms can only grow crops for a few years in the poor soil. The farmers then sell the land to a cattle rancher or just leave and clear a new piece of land. The soil is so poor that it will not even grow grass to feed cattle for more than a few more years. By then, the ground is hard packed and grows only a few weeds. The rain forest is destroyed and nothing can be done with the land.
If this continues long enough, the forests will be destroyed and the farmers will have no place to move. Then those people will, because there will be no land left where they can grow food. Forcing them to stop cutting down the forest will not help, because they would just starve now instead of later. New ways need to be found for these people to live on the rain forest land without destroying it.
Also, no one knows how destroying the rain forests will change the earth. We know that less rain will fall once the trees are gone. That may cause some rivers, which supply water to cities around the rain forest, to dry up during part of the year. Also, burning trees puts carbon into the air. Carbon absorbs heat from the sun. Will the burning of so many trees change the air and make the climate on the earth warmer? Experts are arguing about it, but it might be happening.
The rain forests are also the source of many things that are useful to human beings. As many as one out of every four drugs bought at the store were discovered in rain forest. Coffee, chocolate, bananas, corn, tea, sweet potatoes, Brazil nuts, rubber, and tapioca all came from the rain forest. Very valuable wood is taken from the trees of the rain forest. Mahogany, teak, and balsa wood come from there. Thos etrees can not be grown without the thick, wet, warm rain forests. Thus, the loss of the rain forests would hurt other people besides those that must live there.
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