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The Amazon Rainforest

The Amazon rainforest,[a] also called Amazon jungle or Amazonia, is a moist broadleaf tropical rainforest in the Amazon biome that covers most of the Amazon basin of South America. This basin encompasses 7,000,000 km2 (2,700,000 sq mi), of which 5,500,000 km2 (2,100,000 sq mi) are covered by the rainforest. This region includes territory belonging to nine nations and 3,344 formally acknowledged indigenous territories.

the amazon rainforest

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The majority of the forest, 60%, is in Brazil, followed by Peru with 13%, Colombia with 10%, and with minor amounts in Bolivia, Ecuador, French Guiana, Guyana, Suriname, and Venezuela. Four nations have "Amazonas" as the name of one of their first-level administrative regions, and France uses the name "Guiana Amazonian Park" for French Guiana's protected rainforest area. The Amazon represents over half of the planet's remaining rainforests,[2] and comprises the largest and most biodiverse tract of tropical rainforest in the world, with an estimated 390 billion individual trees in about 16,000 species.[3]

The rainforest likely formed during the Eocene era (from 56 million years to 33.9 million years ago). It appeared following a global reduction of tropical temperatures when the Atlantic Ocean had widened sufficiently to provide a warm, moist climate to the Amazon basin. The rainforest has been in existence for at least 55 million years, and most of the region remained free of savanna-type biomes at least until the current ice age when the climate was drier and savanna more widespread.[14][15]

There is evidence that there have been significant changes in the Amazon rainforest vegetation over the last 21,000 years through the last glacial maximum (LGM) and subsequent deglaciation. Analyses of sediment deposits from Amazon basin paleolakes and the Amazon Fan indicate that rainfall in the basin during the LGM was lower than for the present, and this was almost certainly associated with reduced moist tropical vegetation cover in the basin.[20] In present day, the Amazon receives approximately 9 feet of rainfall annually. There is a debate, however, over how extensive this reduction was. Some scientists argue that the rainforest was reduced to small, isolated refugia separated by open forest and grassland;[21] other scientists argue that the rainforest remained largely intact but extended less far to the north, south, and east than is seen today.[22] This debate has proved difficult to resolve because the practical limitations of working in the rainforest mean that data sampling is biased away from the center of the Amazon basin, and both explanations are reasonably well supported by the available data.

More than 56% of the dust fertilizing the Amazon rainforest comes from the Bodélé depression in Northern Chad in the Sahara desert. The dust contains phosphorus, important for plant growth. The yearly Sahara dust replaces the equivalent amount of phosphorus washed away yearly in Amazon soil from rains and floods.[23]

For a long time, it was thought that the Amazon rainforest was never more than sparsely populated, as it was impossible to sustain a large population through agriculture given the poor soil. Archeologist Betty Meggers was a prominent proponent of this idea, as described in her book Amazonia: Man and Culture in a Counterfeit Paradise. She claimed that a population density of 0.2 inhabitants per square kilometre (0.52/sq mi) is the maximum that can be sustained in the rainforest through hunting, with agriculture needed to host a larger population.[31] However, recent anthropological findings have suggested that the region was actually densely populated. Some 5 million people may have lived in the Amazon region in AD 1500, divided between dense coastal settlements, such as that at Marajó, and inland dwellers.[32] By 1900, the population had fallen to 1 million and by the early 1980s it was less than 200,000.[32]

Wet tropical forests are the most species-rich biome, and tropical forests in the Americas are consistently more species rich than the wet forests in Africa and Asia.[40] As the largest tract of tropical rainforest in the Americas, the Amazonian rainforests have unparalleled biodiversity. One in ten known species in the world lives in the Amazon rainforest.[41] This constitutes the largest collection of living plants and animal species in the world.

The region is home to about 2.5 million insect species,[42] tens of thousands of plants, and some 2,000 birds and mammals. To date, at least 40,000 plant species,[43] 2,200 fishes,[44] 1,294 birds, 427 mammals, 428 amphibians, and 378 reptiles have been scientifically classified in the region.[45] One in five of all bird species are found in the Amazon rainforest, and one in five of the fish species live in Amazonian rivers and streams. Scientists have described between 96,660 and 128,843 invertebrate species in Brazil alone.[46]

The biodiversity of plant species is the highest on Earth with one 2001 study finding a quarter square kilometer (62 acres) of Ecuadorian rainforest supports more than 1,100 tree species.[47] A study in 1999 found one square kilometer (247 acres) of Amazon rainforest can contain about 90,790 tonnes of living plants. The average plant biomass is estimated at 356 47 tonnes per hectare.[48] To date, an estimated 438,000 species of plants of economic and social interest have been registered in the region with many more remaining to be discovered or catalogued.[49] The total number of tree species in the region is estimated at 16,000.[3]

The green leaf area of plants and trees in the rainforest varies by about 25% as a result of seasonal changes. Leaves expand during the dry season when sunlight is at a maximum, then undergo abscission in the cloudy wet season. These changes provide a balance of carbon between photosynthesis and respiration.[50]

The rainforest contains several species that can pose a hazard. Among the largest predatory creatures are the black caiman, jaguar, cougar, and anaconda. In the river, electric eels can produce an electric shock that can stun or kill, while piranha are known to bite and injure humans.[51] Various species of poison dart frogs secrete lipophilic alkaloid toxins through their flesh. There are also numerous parasites and disease vectors. Vampire bats dwell in the rainforest and can spread the rabies virus.[52] Malaria, yellow fever and dengue fever can also be contracted in the Amazon region.

In the 1970s, construction began on the Trans-Amazonian highway. This highway represented a major threat to the Amazon rainforest.[62] The highway still has not been completed, limiting the environmental damage.

Between 1991 and 2000, the total area of forest lost in the Amazon rose from 415,000 to 587,000 km2 (160,000 to 227,000 sq mi), with most of the lost forest becoming pasture for cattle.[63] Seventy percent of formerly forested land in the Amazon, and 91% of land deforested since 1970, have been used for livestock pasture.[64][65] Currently, Brazil is the largest global producer of soybeans. New research however, conducted by Leydimere Oliveira et al., has shown that the more rainforest is logged in the Amazon, the less precipitation reaches the area and so the lower the yield per hectare becomes. So despite the popular perception, there has been no economical advantage for Brazil from logging rainforest zones and converting these to pastoral fields.[66]

The needs of soy farmers have been used to justify many of the controversial transportation projects that are currently developing in the Amazon. The first two highways successfully opened up the rainforest and led to increased settlement and deforestation. The mean annual deforestation rate from 2000 to 2005 (22,392 km2 or 8,646 sq mi per year) was 18% higher than in the previous five years (19,018 km2 or 7,343 sq mi per year).[67] Although deforestation declined significantly in the Brazilian Amazon between 2004 and 2014, there has been an increase to the present day.[68]

Since the discovery of fossil fuel reservoirs in the Amazon rainforest, oil drilling activity has steadily increased, peaking in the Western Amazon in the 1970s and ushering another drilling boom in the 2000s.[69] Oil companies have to set up their operations by opening new roads through the forests, which often contributes to deforestation in the region.[70]

One computer model of future climate change caused by greenhouse gas emissions shows that the Amazon rainforest could become unsustainable under conditions of severely reduced rainfall and increased temperatures, leading to an almost complete loss of rainforest cover in the basin by 2100.[84][85], and severe economic, natural capital and ecosystem services impacts of not averting the tipping point.[86] However, simulations of Amazon basin climate change across many different models are not consistent in their estimation of any rainfall response, ranging from weak increases to strong decreases.[87] The result indicates that the rainforest could be threatened through the 21st century by climate change in addition to deforestation.

In 1989, environmentalist C.M. Peters and two colleagues stated there is economic as well as biological incentive to protecting the rainforest. One hectare in the Peruvian Amazon has been calculated to have a value of $6820 if intact forest is sustainably harvested for fruits, latex, and timber; $1000 if clear-cut for commercial timber (not sustainably harvested); or $148 if used as cattle pasture.[88]

According to WWF, ecotourism could help the Amazon to reduce deforestation and climate change. Ecotourism is currently still little practiced in the Amazon, partly due to lack of information about places where implementation is possible. Ecotourism is a sector that can also be taken up by the Indigenous community in the Amazon as a source of income and revenue. An ecotourism project in the Brazilian-section of the Amazon rainforest had been under consideration by Brazil's State Secretary for the Environment and Sustainable Development in 2009, along the Aripuanã river, in the Aripuanã Sustainable Development Reserve.[89] Also, some community-based ecotourism exists in the Mamirauá Sustainable Development Reserve.[90] Ecotourism is also practiced in the Peruvian-section of the Amazon rainforest. A few ecolodges are for instance present between Cusco and Madre de Dios.[91] 041b061a72


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