Friday, January 14, 2011
Rainforests are forest 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.
A total of 40 to 75% of all species on the world's habitats are indegenous to the rainforests. It has been estimated that many millions of species of plants, insects, and microorganism 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 tress called a jungle. There are two types of rainforest,tropical rainforest and temperate rainforest.
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, butterfly, 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 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 Beededeclared 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 canopy is still in its infancy, but other methods include the use of ballons 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 constrictor, 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% 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% 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
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. Five million years from now, the Amazon rainforest will have long since dried and transformed itself into a savannah; killing itself in the progress (even if all human deforestation activity ceases overnight). The descendants of our known animals will adapt to the dry savannah of the former Amazonian rainforest and thrive in the new, warmer temperatures.