Rainforests are forests that are characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm (68-78 inches). The monsoon trough - alternatively known as the inter-tropical convergence zone - plays a significant role in creating the climatic conditions necessary for the Earth's tropical rainforests.
Around 40% to 75% of all biotic species are indigenous to the rainforests. In fact it has been estimated that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests. Tropical rainforests have been called the 'Jewels of the Earth' and the 'World's Largest Pharmacy'. Why? Because over one quarter of natural medicines have been discovered here.
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 plants and animals. Many rainforest species are rapidly disappearing due to deforestation, habitat loss and pollution of the atmosphere.
The undergrowth in a rainforest is restricted in many areas by the poor penetration of sunlight to ground level. This makes it easy to walk through an undisturbed, mature rainforest. 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.
WHAT IS THE RAIN FOREST MADE UP OF?
A tropical rainforest is typically divided into four main layers, each with different plants and animals adapted for life in that particular area. These layers are as follows:
1. The Emergent layer
The emergent layer contains a small number of very large trees called emergents, which grow above the general canopy, reaching heights of 45–55m, although on occasion a few species will grow to 70–80m tall. They need to be able to withstand the hot temperatures and strong winds that occur above the canopy in some areas. Eagles, butterflies, bats and certain monkeys inhabit this layer.
2. The Canopy 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.
3. Under-storey or under-canopy layer
Many seedlings that will grow to the canopy level are present in the under-storey. Only about 5% of the sunlight shining on the rainforest canopy reaches the under-storey. This layer can be called a shrub layer, although the shrub layer may also be considered a separate layer.
4. Forest floor or shrub layer
The forest floor, the bottom-most layer, receives only 2% of the 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, because the warm, humid conditions promote rapid decay. Many forms of fungi growing here help decay the animal and plant waste.
What is often not realised is that rainforests benefit everyone, and not just the local populations of where they are found. Rainforests store water, regulate rainfall, and are home to over half the planets biodiversity, but more importantly they play a critical role in helping to limit the amount of fossil fuel emissions that build up in our atmosphere every year by absorbing CO2 as part of their normal photosynthetic process. The trouble is that when they are cut down and burned, not only are they then unable to absorb these emissions, they actually release yet more CO2 into the atmosphere. Currently, rainforest destruction accounts for 17% of global CO2 emissions which is more than the global transport sector releases.
Why is the rainforest being destroyed?
Despite what some government groups are trying to promote, human greed is the main cause of rainforest deforestation. Incredibly, between May 2000 and August 2005, Brazil lost more than 132,000 square kilometres of forest — an area larger than Greece — and since 1970, over 600,000 square kilometres (232,000 square miles) of Amazon rainforest have been destroyed.
But what are the reasons behind why so much rainforest habitat is being systematically cut down and burned?
Well, here are a number of obvious causes, such as wood being used for the worlds timber magnets, land clearance for farming and road construction.
For several years now, the Brazilian government has insisted that the rate of deforestation in the Amazon has declined sharply. But earlier this year, it suddenly jumped again, to a rate five times higher than last year.
These trees play a vital part in the management of global weather patterns. Why? Because they absorb carbon dioxide, which otherwise would contribute to climate change. That is why Brazil is under pressure to protect the forest.
Perhaps the biggest threat to the Amazon rain forest are the Amazon settlers as they burn down the trees to clear land for cattle.
Amazon settler Waldemar Vieira Neves understands this, but he says there are other considerations as well. He is is a small, wiry man, 64 years old, with sharp features and a deep sense of grievance.
‘…I know everyone thinks we're villains, but what people don't understand is how hard we have to work to scratch out a living. We were talking in a small clearing in the forest…’
He used to live in the far north-east of Brazil, with no land and not much hope.
So, like tens of thousands of other settlers, he took the opportunity and did what the government wanted him to do - made a new home for himself in the forest and cleared the trees.
Nowadays, Brazil's laws on deforestation are extremely strict.
No-one who farms in the rainforest is supposed to be allowed to cultivate more than 20% of the land he owns. The rest has to be left untouched, as a way of preserving the forest and protecting the environment.
But sometimes, says Waldemar, people feel they have to break the law. What else can you do if there is no other way to survive?
‘…people say we're destroying the forest, we're not. We're protecting it, we depend on it. But we have to find a way so that both we and the forest can survive…’
The settlers complain that they need more help in finding ways to make a living while keeping on the right side of the law.
Within the next few months, Brazilian President Dilma Rousseff, who came to office six months ago, will have to decide whether to veto proposals to relax the Forest Code, which restricts how much land in the Amazon region can legally be cultivated.
Farmers and big international agricultural business groups say they need to be able to farm more land to provide the food that the world demands.
They want an amnesty for farmers who may have cleared forest land illegally in the past, proposing that - instead of being fined - farmers who have broken the law should be required to buy more forest, equivalent to what they have cut down, in return for an undertaking to leave it untouched.
Brazil now exports more beef than any other country in the world, and agriculture makes up a quarter of the country's entire economic output.
It is also the world's second biggest producer of soya, which is an essential ingredient in animal feed, and pressure from the huge soya producers south of the Amazon who are desperate to buy more land is pushing smaller farmers like Waldemar Vieira Neves deeper into the forest.
On the one hand, President Rousseff does not want to risk jeopardising Brazil's rapid economic growth by damaging its powerful agri-business interests. On the other, she is under intense pressure from environmentalists not to approve any law that could encourage more deforestation in the Amazon.
Before her election last year, she pledged to veto any plan that would weaken the Forest Code and, within the coming months, she is going to have to decide whether to honour that pledge.
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