| • Science | • People | • Locations | • Timeline |
Rain forests are home to two-thirds of all the living animal and plant species on the planet. Billions of new species of plants, insects, and microorganisms are still undiscovered and have no names yet. Tropical rain forests are called the 'jewel of the earth', the 'Earth’s lungs', and the 'world's largest pharmacy' because of the large amount of natural medicines discovered there. Nearly half of the medicines we use come from the rainforests. Scientists believe that the cures for many more diseases will be discovered there in the future.
Despite the growth of flora in a rainforest, the actual quality of the soil is quite poor. Oxisols, infertile, deeply weathered and severely leached, have developed on the ancient Gondwanan shields. Rapid bacterial decay prevents the accumulation of humus. The concentration of iron and aluminum 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 humans 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.
There are several common characteristics of tropical trees. Tropical species frequently possess one or more of the following attributes not seen in trees of higher latitudes.
Buttresses: many species have broad, woody flanges at the base of the trunk. Originally believed to help support the tree, now it is believed that the buttresses channel stem flow and its dissolved nutrients to the roots. Large leaves are common among trees of the C layer. Young individuals of trees destined for the B and A layers may also have large trees. When the reach the canopy new leaves will be smaller. The large leaf surface helps intercept light in the sun-dappled lower strata of the forest. Drip tips facilitate drainage of precipitation off the leaf to promote transpiration. They occur in the lower layers and among the saplings of species of the emergent layer (A layer). Trees are often well connected in the canopy layer especially by the growth of woody climbers or lianas. Plants with epiphytic adaptations, allowing them to grow on top of existing trees in the competition for sunlight.
Other characteristics that distinguish tropical species of trees from those of temperate forests include
Exceptionally thin bark, often only 1-2 mm thick. Usually very smooth, although sometimes armed with spines or thorns. Cauliflory, the development of flowers (and hence fruits) directly from the trunk, rather than at the tips of branches. Large fleshy fruits attract birds, mammals, and even fish as dispersal agents.
It is estimated that rainforests provide up to 40% of the oxygen currently found in the atmosphere. And yet, tropical and temperate rain forests have been subjected to heavy logging and agricultural clearance throughout the 20th century, so that the area covered by rainforest around the world is rapidly shrinking. It is estimated that the rainforest was reduced by about 58,000 km² annually in the 1990s. Rainforests used to cover 14% of the Earth's surface. This percentage is now down to 6% and it is estimated that the remaining rainforests could disappear within 40 years (mid-21st century) at the present rate of logging. Many scientists seriously dispute these estimates, especially considering the rapid growth of new tropcial rainforests in cleared areas. Biologists have estimated that large numbers of species are being extirpated (driven to extinction)—possibly more than 50,000 a year—due to the removal of habitat with destruction of the rain forests. Organizations like the Arbor Day Foundation use donation money to protect the rain forest trees from logging.
The largest tropical rainforests exist in the Amazon basin (the Amazon RainforestThe Amazon is a rainforest in South America. It encompasses 1. 2 billion acres (5 million km²), with parts located within nine nations: Brazil, Colombia, Peru, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French Guiana. This forest represents over ha), in the equatorial portions of the Democratic Republic of Congo, and in much of IndonesiaThe Republic of Indonesia the world's largest archipelago, is located between the Southeast Asian peninsula and Australia, between the Indian and Pacific Oceans. Indonesia borders Malaysia on the island of Borneo ( Kalimantan in Bahasa Indonesia), Papua N. Temperate rainforests are found along the Pacific coast of North America from AlaskaOn January 3, 1959, Alaska was admitted to the United States as the 49th state. The population of the state is 626,932, as of 2000. The name "Alaska" is most likely derived from the Aleut word for "great country" or "mainland. The natives called it "Alyes through WashingtonWashington is a state in the Pacific Northwest of the United States. It should not be confused with Washington, DC, the nation's capital. To avoid confusion, the state is often called Washington state . Although the state capital is Olympia, the largest c state, in the former YugoslaviaYugoslavia Jugoslavija in all south Slavic languages) is a term used for three separate political entities that existed during most of the 20th century. Translated, the name means Land of the South Slavs jug in Jugoslavija means south). The first was a ki, and in parts of JapanJapan (, Nippon/Nihon literally "the origin of the sun") is a country in East Asia situated on a chain of islands east of the Asian continent on the western edge of the Pacific Ocean. The largest of these islands are, from north to south, Hokkaido , Honsh. Most temperate rainforests result from prevailing upslope flow along a mountain range.