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Rain Forest
Jungle and rain forest are terms that are often used synonymously but with little precision. The more meaningful and restrictive of these terms is rain forest, which refers to the climax or primary forest in regions with high rainfall (greater than 1.8 m/70 in per year), chiefly but not exclusively found in the tropics. Rain forests are significant for their valuable timber resources, and in the tropics they afford sites for commercial crops such as rubber, tea, coffee, bananas, and sugarcane. They also include some of the last remaining areas of the Earth that are both unexploited economically and inadequately known scientifically. The term jungle originally referred to the tangled, brushy vegetation of lowlands in India, but it has come to be used for any type of tropical forest or woodland. The word is more meaningful if limited to the dense, scrubby vegetation that develops when primary rain forest has been degraded by destructive forms of logging or by cultivation followed by abandonment. Types of Rain Forest Rain forests may be grouped into two major types: tropical and temperate. Tropical rain forest is characterized by broadleaf evergreen trees forming a closed canopy, an abundance of vines and epiphytes (plants growing on the trees), a relatively open forest floor, and a very large number of species of both plant and animal life. The largest trees have buttressed trunks and emerge above the continuous canopy, while smaller trees commonly form a layer of more shade-tolerant species beneath the upper canopy. The maximum height of the upper canopy of tropical rain forests is generally about 30 to 50 m (100 to 165 ft), with some individual trees rising as high as 60 m (200 ft) above the forest floor. The largest areas of tropical rain forest are in the Amazon basin of South America, in the Congo basin and other lowland equatorial regions of Africa, and on both the mainland and the islands off Southeast Asia, where they are especially abundant on Sumatra and New Guinea. Small areas are found in Central America and along the Queensland coast of Australia. Temperate rain forests, growing in higher-latitude regions having wet, maritime climates, are less extensive than those of the tropics but include some of the most valuable timber in the world. Notable forests in this category are those on the northwest coast of North America, in southern Chile, in Tasmania, and in parts of southeastern Australia and New Zealand. These forests contain trees that may exceed in height those of tropical rain forests, but there is less diversity of species. Conifers such as REDWOOD and Sitka spruce tend to predominate in North America, while their counterparts in the southern hemisphere include various species of EUCALYPTUS, Araucaria, and Nothofagus (Antarctic beech). Ecology Rain forests cover less than six percent of the Earth's total land surface, but they are the home for up to three-fourths of all known species of plants and animals; undoubtedly they also contain many more species as yet undiscovered. Recent studies suggest that this great diversity of species is related to the apparently dynamic and unstable nature of rain forests over geologic time. The fact is that despite their appearance of fertile abundance, rain forests are fragile ecosystems. Their soils can quickly lose the ability to support most forms of vegetation once the forest cover is removed, and some soils even turn into hard LATERITE clay. The effect of forest removal on local climates is also often profound, although the role of rain forests in world climatic changes is not yet clear. Humans and Rain Forests Throughout history, human beings have encroached on rain forests for living space, timber, and agricultural purposes. In vast portions of upland tropical forest, for example, the practice of "shifting cultivation" has caused deterioration of the primary forest. In this primitive system of agriculture, trees are killed in small plots that are cropped for two or three seasons and then abandoned; if the plots are again cultivated before primary vegetation has reestablished itself, the result is a progressive deterioration of the forest, leading to coarse grass or jungle. Lowland forests are similarly being reduced in many areas; on the island of Java, the lowland primary forest has been almost totally removed and replaced with rice fields or plantation crops such as rubber. In the 20th century these incursions on rain forests have grown rapidly, and numerous organizations are now attempting to reduce the rate of the loss. Bibliography: Caufield, Catherine, In the Rainforest (1985); Forsyth, Adrian, and Miyata, Ken, Tropical Nature: Life and Death in the Rain Forests of Central and South America (1984); Sutton, S. L., et al., Tropical Rain Forest: Ecology and Management (1984); Whitmore, T. C., Tropical Rain Forests of the Far East, 2d. ed. (1984).

 



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