Rainforests

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, eastern Queensland, Australia and in some parts of the United States. Outside of the tropics, temperate rainforests can be found in British Columbia, southeastern Alaska, western Oregon and Washington, Scotland and Norway, the western Caucasus (Ajaria region of Georgia), parts of the western Balkans, New Zealand, Tasmania, and parts of eastern Australia.

In contradiction to popular belief rainforests are not major consumers of carbon dioxide and like all mature forests are approximately carbon neutral [1] [2]. Recent evidence suggests that the majority of rainforests are in fact net carbon emmiters. However rainforests do play a major role in the global carbon cycle as stable carbon pools and clearance of rainforest leads to increased levels of atmospheric carbon dioxide. Rainforests may also play a role in cooling air that passes through them. As such rainforests are of vital importance within the global climate system.

Rainforests are characterized by high rainfall, with definitions setting minimum normal annual rainfall between 2000 mm and 1750mm

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 "jewel of the earth", and the "world's largest pharmacy" because of the large amount of natural medicines discovered there. Rainforests are also often described as the "Earth's lungs", however this appellation has no scientific basis as rainforests produce little or no net oxygen [3].

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.

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 colonised by a dense tangled growth of vines, shrubs and small trees called jungle.