tropical rainforestTropical rainforest in Malaysia.(more)The Earth’s magnificent tropical rainforests represent a treasure trove of biological heritage. They not only retain many primitive plant and animal species with incredible and ancient evolutionary lineages but are also communities that exhibit unparalleled biodiversity and a great variety of ecological interactions. The tropical rainforests of Africa, for example, were the habitat in which the ancestors of humans evolved and are where our nearest surviving relatives—chimpanzees and gorillas—live still. Tropical rainforests have long supplied a rich variety of food and other resources to Indigenous peoples, who, for the most part, make use of this bounty without degrading the vegetation or reducing its range. Rainforests provide a wide array of ecosystem services, including the provision of basic human needs, such as timber and food; cultural services with recreational, aesthetic, or spiritual benefits; and vital ecological services, such as nutrient cycling, oxygen production, wildlife habitat, erosion and flood control, water filtration, and carbon sequestration. While it covers just 2 percent of Earth’s surface, the dense vegetation of these forests plays an important role in the health of our planet. Unfortunately, thousands and thousands of acres of the world’s rainforests are destroyed each day, as trees are cut down for wood and land is cleared for agriculture.

　　Biodiversity

　　terrestrial hot spots of biodiversityMoist tropical forests such as the Amazon Rainforest are considered biodiversity hot spots and have the greatest concentrations of animal and plant species of any terrestrial ecosystem. Perhaps two-thirds of Earth’s species live exclusively in these forests, though only a minority of these species have been formally described and scientifically named. According to some informed estimates, more than a hundred species of rainforest fauna and flora become extinct every week as a result of widespread clearing of forests by humans. Insects are believed to constitute the greatest percentage of disappearing species.

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　　Carbon sequestration

　　Amazon deforestation: slash-and-burnSlash-and-burn forest clearing in the Amazon.(more)Forests of all types are the largest carbon reservoirs on land. In terrestrial communities, up to 80 percent of the aboveground carbon and about a third of belowground carbon are contained within forests. It is estimated that tropical rainforests serve as sinks for more than 50 percent of all atmospheric carbon dioxide absorbed by plants annually. Forests sequester carbon in the form of wood and other biomass as the trees grow, taking up carbon dioxide from the atmosphere (see carbon cycle). When rainforests are slashed and burned, their carbon is returned to the atmosphere as carbon dioxide, a potent greenhouse gas that is one of the key drivers of anthropogenic climate change, and the trees are no longer present to sequester more carbon. Deforestation in tropical areas thus has major global implications, and rainforest conservation and reforestation constitute a significant climate-change mitigation strategy.

　　Water and oxygen The role that rainforests play at the global level in weather, climate change, oxygen production, and carbon cycling, while significant, is only just beginning to be appreciated. For instance, tropical rainforests play an important role in the exchange of gases between the biosphere and atmosphere, and their role as “the lungs of the Earth” in terrestrial oxygen production is well known. In the upper Amazon River basin of South America, the rainforest recycles rains brought primarily by easterly trade winds. Indeed, surface transpiration and evaporation supply about half of the rainfall for the entire region, and in basins of dense forest far from the ocean such local processes can account for most of the local rainfall. Should the Amazon Rainforest, which accounts for 30 percent of the land area in the equatorial belt, disappear, drought would likely follow, and the global energy balance might well be affected. Given their incredible biomass, rainforests throughout the world can absorb huge amounts of water. When rainforests are destroyed, the vast amounts of rainfall in those regions cannot be absorbed, resulting in widespread flooding and soil erosion.

　　Pharmaceuticals and other natural products

　　natural rubber Latex being extracted from a rubber tree.(more)Rainforest plants produce an untold number of phytochemicals that may be useful to humans. Numerous medicines, as much as one-quarter of all prescription drugs, have been made from materials gathered in rainforests—including cocaine and quinine—and many more lifesaving pharmaceuticals may await discovery there. Rainforest plants have also been used to make plant-based insecticides that are far less toxic than synthetic, or human-made, chemicals. Many products, such as natural rubber, essential oils used in cosmetics and perfumes, rattan (a material woven together to make furniture), and a number of food products such as acai and Brazil nuts, can be sustainably harvested from rainforests without causing widespread destruction.

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