Rainforests, or rain forests, are forests characterized by high rainfall, with definitions setting minimum normal annual rainfall between 1750 mm and 2000 mm (68 inches to 78 inches).
Rainforests are home to two thirds of all the living animal and plant species on the planet. It has been estimated that many hundreds of millions of new species of plants, insects and microorganisms are still undiscovered. Tropical rain forests are called the "jewels of the earth", and the "world's largest pharmacy" because of the large number of natural medicines discovered there. Tropical rain forests are also often called the "Earth's lungs", however there is no scientific basis for such a claim as tropical rainforests are known to be essentially oxygen neutral, with little or no net oxygen production.
The undergrowth in a rainforest is restricted in many areas by the lack of sunlight at ground level. This makes it possible for people and other animals to walk through the forest. If the leaf canopy is destroyed or thinned for any reason, the ground beneath is soon colonized by a dense tangled growth of vines, shrubs and small trees called a jungle.
The largest tropical rainforests exist in the Amazon Basin (the Amazon Rainforest), in Nicaragua (Los Guatuzos, Bosawás and Indio-Maiz), the southern Yucatán Peninsula-El Peten-Belize contiguous area of Central America (including the Calakmul Biosphere Reserve), in much of equatorial Africa from Cameroon to the Democratic Republic of Congo, in much of southeastern Asia from Myanmar to Indonesia and Papua New Guinea, northern and eastern Australia and in the Hawaiian Islands. The majority of tropical rainforest is found within a 20 degree band around the equator.
Outside of the tropics, temperate rainforests can be found in North America including the northwestern coast of the United States, the Pacific coast of Canada, and the interior rainforests of British Columbia's Rocky Mountain Trench east of Prince George. In Europe they are found in coastal portions of Ireland, Scotland and southern Norway, parts of the western Balkans along the Adriatic coast, coastal areas of the eastern Black Sea including Georgia and coastal Turkey. In Asia portions of southern China, Taiwan, much of Japan, Korea, Sakhalin Island and the adjacent coast of Russia.
Despite the growth of vegetation in a rainforest, the actual quality of the soil 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 (e.g. bauxite). On younger substrates, especially of volcanic origin, tropical soils may be quite fertile.
A natural rainforest emits and absorbs vast quantities of carbon dioxide.
Over the long term these fluxes are approximately in balance, so that
an undisturbed rainforest would have little net impact on atmospheric CO2
levels, though they may have other climatic effects (on cloud
formation, for example, by recycling water vapour). No rainforest in
the 21st century 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.
These droughts themselves are believed to be exacerbated by human
induced climate change. Some climate models run with interactive
vegetation 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. Not only that but by 2090 scientists
estimate that all rainforests will have disappeared at the rate we are deforesting them.
The rainforest is divided into four different parts, each with different plants and animals, adapted for life in that particular area.
This layer contains a small number of very large trees which grow above the general canopy, reaching heights of 45-55 m, although on occasion a few species will grow to 70 m or 80 m tall.They need to be able to withstand the hot temperatures and strong winds. 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% of all plant species, suggesting that perhaps half of all life on Earth could be found there. 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, U.S. 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.
There is a space between the canopy and the forest floor, which is known as the understory (or understorey). This 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% of the sunlight shining on the rainforest reaches the understory. This layer can also be called a shrub layer although some have a perception that the shrub layer is an individual layer.
This region receives only 2% of the rainforest's sunlight, thus only specially adapted plants can grow in this region. Away from river banks, swamps and clearings where dense undergrowth is found, the forest floor is relatively clear of vegetation, as little sunlight penetrates to ground level. 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. This amounts to over 5 million species of plants and animals.
There is less likelihood of your rescue from beneath a dense jungle
canopy than in other survival situations. You will probably have to
travel to reach safety.
With practice, movement through thick undergrowth and jungle can be
done efficiently. Always wear long sleeves to avoid cuts and scratches.
Pinpoint your initial location as accurately as possible to determine a general line of travel to safety. If you do not have a compass, use a field-expedient direction finding method.
Take stock of water supplies and equipment.
Move in one direction, but not necessarily in a straight line. Avoid obstacles. In enemy territory, take advantage of natural cover and concealment.
Move smoothly through the jungle. Do not blunder through it since you will get many cuts and scratches. Turn your shoulders, shift your hips, bend your body, and shorten or lengthen your stride as necessary to slide between the undergrowth.