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 intertropical 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 are also responsible for 28% of the world's oxygen turnover, sometimes misnamed oxygen production, processing it through photosynthesis from carbon dioxide and consuming it through respiration.
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 45–55 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 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. Understorey or undercanopy layer
Many seedlings that will grow to the canopy level are present in the understorey. Only about 5% of the sunlight shining on the rainforest canopy reaches the understorey. 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.
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Based on an article by http://en.wikipedia.org/wiki/Rainforest
Photo care of http://article.wn.com/view/2009/02/13/Government_to_tap_Brazils_agriculture_expertise/ and
http://www.geography.learnontheinternet.co.uk/topics/rainforest.html and http://amazonrainforestanimalsfacts.blogspot.com/ and http://true-wildlife.blogspot.com/2011/02/chameleon.html