Dense forest usually found on or near the Equator where the climate is hot and wet. There are two types of rainforest, tropical and temperate, although the former are much more common. Moist air brought by the converging trade winds rises because of the heat and produces heavy rainfall. More than half the tropical rainforests are in Central and South America, primarily the lower Amazon and the coasts of Ecuador and Columbia. The rest are in Southeast Asia (Malaysia, Indonesia, and New Guinea) and in West Africa and the Congo. Temperate rainforests are found in temperate regions such as western North America, southern Chile, Norway, and New Zealand. It is estimated that around 50% of the plants and animals on Earth live in rainforests.
Tropical rainforests once covered 10% of the Earth's land surface, but are now being destroyed at an increasing rate as their valuable timber is harvested and the land cleared for agriculture, causing problems of deforestation and climate change. By 2014, tropical rainforests covered only 5–6% of the Earth's land surface.
The vegetation in tropical rainforests typically includes an area of dense forest called selva; a canopy formed by high branches of tall trees providing shade for lower layers; an intermediate layer of shorter trees and tree roots; lianas; and a ground cover of mosses and ferns. The lack of seasonal rhythm causes adjacent plants to flower and shed leaves simultaneously. Chemical weathering and leaching take place in the iron-rich soil due to the high temperatures and humidity.
Rainforests contain some of the highest levels of biodiversity and comprise some of the most complex and diverse ecosystems on the planet. In a hectare (10,000 sq m/107,640 sq ft) of rainforest there are an estimated 200–300 tree species compared with 20–30 species in a hectare of temperate forest. The trees are the main producers. Herbivores such as insects, caterpillars, and monkeys feed on the plants and trees and in turn are eaten by the carnivores, such as ocelots and puma. Fungi and bacteria, the primary decomposers, break down the dead material from the plants, herbivores, and carnivores with the help of heat and humidity. This decomposed material provides the nutrients for the plants and trees.
The rainforest ecosystem helps to regulate global weather patterns – especially by taking up CO2 (carbon dioxide) from the atmosphere – and stabilizes the soil. Rainforests provide most of the oxygen needed for plant and animal respiration. When deforestation occurs, the microclimate of the mature forest disappears; soil erosion and flooding become major problems since rainforests protect the deep tropical soils. Once an area is cleared it is very difficult for shrubs and bushes to re-establish because soils are poor in nutrients. This causes problems for plans to convert rainforests into agricultural land – after two or three years the crops fail and the land is left bare. Clearing of the rainforests releases carbon dioxide into the atmosphere and reduces the forests' absorption of carbon dioxide. This contributes to the greenhouse effect and may significantly contribute to global warming.
Tropical rainforests are characterized by a great diversity of species, usually of tall broad-leafed evergreen trees, with many climbing vines and ferns, some of which are a potential source of raw materials for the development of new medicines. A tropical forest, if properly preserved, can yield medicinal plants, oils (from cedar, juniper, cinnamon, sandalwood), spices, gums, resins (used in inks, lacquers, linoleum), tanning and dyeing materials, forage for animals, beverages, poisons, green manure, rubber, and animal products (feathers, hides, honey). Other types of rainforest include montane, upper montane or cloud, mangrove, and subtropical.
Traditional ways of life in tropical rainforests are disappearing. The practice of shifting cultivation (slash and burn), in which small plots of forest are cultivated and abandoned after two or three harvests, is being replaced by cultivation on such a large scale that the rainforests cannot regenerate. As a result hunting and gathering as a way of life is also becoming less viable. In the last 30 years, Central America has lost almost two-thirds of its rainforests to cattle ranching.
Ecosystems: Tropical Rainforests
Extinction: A Race against Time
The Fate of the Rainforests
Forests: The Hunt for Sustainability
Destruction of the rainforest and global warming
Functions of the rainforest
Destructioon of the Amazon rainforest
Exploring the Tropics
Manu: Peru's Hidden Rainforest
Rainforests of the World
Warriors of the Amazon
African tulip tree
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