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The Amazon: The World's Largest Rainforest
By Rhett A. Butler [citation]
The Amazon River Basin is home to the largest rainforest on Earth. The basin -- roughly the size of the forty-eight contiguous United States -- covers some 40% of the South American continent and includes parts of eight South American countries: Brazil, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, and Suriname, as well as French Guiana, a department of France.
Reflecting environmental conditions as well as past human influence, the Amazon is made up of a mosaic of ecosystems and vegetation types including rainforests, seasonal forests, deciduous forests, flooded forests, and savannas. The basin is drained by the Amazon River, the world's largest river in terms of discharge, and the second longest river in the world after the Nile. The river is made up of over 1,100 tributaries, 17 of which are longer than 1000 miles, and two of which (the Negro and the Madeira) are larger, in terms of volume, than the Congo (formerly the Zaire) river. The river system is the lifeline of the forest and its history plays an important part in the development of its rainforests.
HISTORY
At one time Amazon River flowed westward, perhaps as part of a proto-Congo (Zaire) river system from the interior of present day Africa when the continents were joined as part of Gondwana. Fifteen million years ago, the Andes were formed by the collision of the South American plate with the Nazca plate. The rise of the Andes and the linkage of the Brazilian and Guyana bedrock shields, blocked the river and caused the Amazon to become a vast inland sea. Gradually this inland sea became a massive swampy, freshwater lake and the marine inhabitants adapted to life in freshwater. For example, over 20 species of stingray, most closely related to those found in the Pacific Ocean, can be found today in the freshwaters of the Amazon.
About ten million years ago, waters worked through the sandstone to the west and the Amazon began to flow eastward. At this time the Amazon rainforest was born. During the Ice Age, sea levels dropped and the great Amazon lake rapidly drained and became a river. Three million years later, the ocean level receded enough to expose the Central American isthmus and allow mass migration of mammal species between the Americas.
The Ice Ages caused tropical rainforest around the world to retreat. Although debated, it is believed that much of the Amazon reverted to savanna and montane forest (see chapter 3-Ice Ages and Glaciation). Savanna divided patches of rainforest into "islands" and separated existing species for periods long enough to allow genetic differentiation (a similar rainforest retreat took place in Africa. Delta core samples suggest that even the mighty Congo watershed was void of rainforest at this time). When the ice ages ended, the forest was again joined and the species that were once one had diverged significantly enough to be constitute designation as separate species, adding to the tremendous diversity of the region. About 6000 years ago, sea levels rose about 130 meters, once again causing the river to be inundated like a long, giant freshwater lake.
THE AMAZON RIVER TODAY
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How large is the Amazon rainforest?
In Brazil, the Amazon covers surface area of 4,100,000 square kilometers (1,583,000 square miles), of which around 3.4 million sq km (1.3 million sq mi) are presently forested. Accounting for parts of the Amazon outside of Brazil, the total extent of the Amazon is estimated at 8,235,430 sq km (3,179,715 sq mi). or comparison, the land area of the United States (including Alaska and Hawaii) is 9,629,091 square kilometers (3,717,811).
In total, the Amazon River drains about 6,915,000 square kilometers (2,722,000 square miles), or roughly 40 percent of South America.
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Today the Amazon River is the most voluminous river on Earth, eleven times the volume of the Mississippi, and drains an area equivalent in size to the United States. During the high water season, the river's mouth may be 300 miles wide and every day up to 500 billion cubic feet of water (5,787,037 cubic feet/sec) flow into the Atlantic. For reference, the Amazon's daily freshwater discharge into the Atlantic is enough to supply New York City's freshwater needs for nine years. The force of the current -- from sheer water volume alone -- causes Amazon River water to continue flowing 125 miles out to sea before mixing with Atlantic salt water. Early sailors could drink freshwater out of the ocean before sighting the South American continent.
The river current carries tons of suspended sediment all the way from the Andes and gives the river a characteristic muddy whitewater appearance. It is calculated that 106 million cubic feet of suspended sediment are swept into the ocean each day. The result from the silt deposited at the mouth of the Amazon is Majaro island, a river island about the size of Switzerland.
(NEXT Amazon rainforest ecology)
Recent news on the Amazon
Fungus from the Amazon devours plastic
(02/02/2012)
Students from Yale University have made the amazing discovery of a species of fungus that devours one of the world's most durable, and therefore environmentally troublesome, plastics: polyurethane. The new species of fungus, Pestalotiopsis microspora, is even able to consume polyurethane in zero-oxygen (anaerobic) conditions, which would be important in eating plastics in the deep dark layers of landfills where little sunlight, water, or oxygen is found.
Photo of the day: super-abundance of life found in Amazon park
(02/02/2012)
Surveying a little-explored park in the Peruvian Amazon has paid off in dividends: researchers with the Wildlife Conservation Society (WCS) have cataloged 365 species that had not yet been recorded in Bahuaja Sonene National Park. The never-before recorded species included two bats, thirty birds, and over two hundred butterflies and moths.
Group releases close-up photos of 'uncontacted' tribe in Peru
(02/01/2012)
New photos provide visual evidence of just how close the long-isolated tribe of Mashco-Piro people in the Amazon rainforest are to being contacted by the outside world—a perilous moment for tribes highly susceptible to disease and likely to defend their people and territory with weapons. According to indigenous rights NGO Survival International, the Maschco-Piro tribe has been seen more frequently outside of their forest home in Manu National Park in recent years. Some experts blame illegal logging in the park and helicopters used in oil and gas projects for the sightings.
New meteorological theory argues that the world's forests are rainmakers
(02/01/2012)
New, radical theories in science often take time to be accepted, especially those that directly challenge longstanding ideas, contemporary policy or cultural norms. The fact that the Earth revolves around the sun, and not vice-versa, took centuries to gain widespread scientific and public acceptance. While Darwin's theory of evolution was quickly grasped by biologists, portions of the public today, especially in places like the U.S., still disbelieve. Currently, the near total consensus by climatologists that human activities are warming the Earth continues to be challenged by outsiders. Whether or not the biotic pump theory will one day fall into this grouping remains to be seen. First published in 2007 by two Russian physicists, Victor Gorshkov and Anastassia Makarieva, the still little-known biotic pump theory postulates that forests are the driving force behind precipitation over land masses.
Saving the world's biggest river otter
(01/30/2012)
Charismatic, vocal, unpredictable, domestic, and playful are all adjectives that aptly describe the giant river otter (Pteronura brasiliensis), one of the Amazon's most spectacular big mammals. As its name suggest, this otter is the longest member of the weasel family: from tip of the nose to tail's end the otter can measure 6 feet (1.8 meters) long. Living in closely-knit family groups, sporting a complex range of behavior, and displaying almost human-like capricious moods, the giant river otter has captured a number of researchers and conservationists' hearts, including Dutch conservationist Jessica Groenendijk.
Big trees, like the old-growth forests they inhabit, are declining globally
(01/26/2012)
Already on the decline worldwide, big trees face a dire future due to habitat fragmentation, selective harvesting by loggers, exotic invaders, and the effects of climate change, warns an article published this week in New Scientist magazine. Reviewing research from forests around the world, William F. Laurance, an ecologist at James Cook University in Cairns, Australia, provides evidence of decline among the world's 'biggest and most magnificent' trees and details the range of threats they face. He says their demise will have substantial impacts on biodiversity and forest ecology, while worsening climate change.
Photo of the Day: Critically Endangered brown spider monkey discovered in park
(01/26/2012)
Researchers with The Wildlife Conservation Society (WCS) and Colombia’s National Parks Unit have located at least two individuals of brown-spider monkey (Ateles hybridus) in Colombia's Selva de Florencia National Park. The discovery is important because its the only known population of this particular subspecies (Ateles hybridus brunneus) in a protected area.
Photos: 46 new species found in little-explored Amazonian nation
(01/25/2012)
South America's tiniest independent nation still hides a number of big surprises: a three week survey to the sourthern rainforests of Suriname found 46 potentially new species and recorded nearly 1,300 species in all. Undertaken by Conservation International's (CI) Rapid Assessment Program (RAP) the survey found new species of freshwater fish, insects, and a new frog dubbed the "cowboy frog" for the spur on its heel. While Suriname may be small, much of its forest, in the Guyana Shield region of the Amazon, remains intact and pristine. The Food and Agriculture Organization (FAO) estimates that 91 percent of Suriname is covered in primary forests, however this data has not been updated in over two decades.
Brazil begins preliminary damming of Xingu River as protests continue
(01/19/2012)
Damming of the Xingu River has begun in Brazil to make way for the eventual construction of the hugely controversial, Belo Monte dam. The Norte Energia (NESA) consortium has begun building coffer dams across the Xingu, which will dry out parts of the river before permanent damming, reports the NGO International Rivers. Indigenous tribes, who have long opposed the dam plans on their ancestral river, conducted a peaceful protest that interrupted construction for a couple hours.
Geology has split the Amazon into two distinct forests
(01/19/2012)
The common view of the Amazon is that it is one massive, unbroken forest. This impression is given by maps which tend to mark the Amazon by a large glob of green or even by its single name which doesn't account for regional changes. Of course, scientists have long recognized different ecosystems in the Amazon, most especially related to climate. But a new study in the Journal of Biogeography has uncovered two distinct forest ecosystems, sharply divided, caused by million of years of geologic forces.
Deforestation, climate change threaten the ecological resilience of the Amazon rainforest
(01/19/2012)
The combination of deforestation, forest degradation, and the effects of climate change are weakening the resilience of the Amazon rainforest ecosystem, potentially leading to loss of carbon storage and changes in rainfall patterns and river discharge, finds a comprehensive review published in the journal Nature.
Peruvian smugglers traffic illegal rainforest timber from Brazil to America
(01/11/2012)
An investigation by Brazil's Federal Police has detailed a significant trade of illegally logged rainforest wood by Peruvian nationals making its way from northern Brazil to the U.S. and Mexico, reports O Globo.
Colonization program remains important driver of deforestation in Brazil
(01/10/2012)
Government-subsidized colonization of the Amazon rainforest remains an important driver of forest loss in Brazil, but has mixed economic value, argues a paper published in Biological Conservation.
As Amazon deforestation falls, food production rises
(01/09/2012)
A sharp drop in deforestation has been accompanied by an increase in food production in the Brazilian state of Mato Grosso, reports a new study published in the journal Proceedings of the National Academy of Science. The research argues that policy interventions, combined with pressure from environmental groups, have encouraged agricultural expansion in already-deforested areas, rather than driving new forest clearing.
Ecuador makes $116 million to not drill for oil in Amazon
(01/02/2012)
A possibly ground-breaking idea has been kept on life support after Ecuador revealed its Yasuni-ITT Initiative had raked in $116 million before the end of the year, breaking the $100 million mark that Ecuador said it needed to keep the program alive. Ecuador is proposing to not drill for an estimated 850 million barrels of oil in the Ishpingo-Tambococha-Tiputinin (ITT) blocs of Yasuni National Park if the international community pledges $3.6 billion to a United Nations Development Fund (UNDF), or about half of what the oil is currently worth. The Yasuni-ITT Initiative would preserve arguably the most biodiverse region on Earth from oil exploitation, safeguard indigenous populations, and keep an estimated 410 million tons of CO2 out of the atmosphere. However, the initiative is not without its detractors, some arguing the program is little more than blackmail; meanwhile proponents say it could prove an effective way to combat climate change, deforestation, and mass extinction.
The year in review for rainforests
(12/28/2011)
2011 was designated as "Year of the Forests" by the United Nations. While there was relatively little progress on intergovernmental forest protection programs during the year, a lot happened elsewhere. Below is a look at some of the biggest tropical forest-related news stories for 2011. We at mongabay readily acknowledge there were a number of important temperate and boreal forest developments, including Britain's decision not to privatize its forests and the severe drought in Texas, but this article will cover only tropical forest news.
Top 10 Environmental Stories of 2011
(12/22/2011)
Many of 2011's most dramatic stories on environmental issues came from people taking to the streets. With governments and corporations slow to tackle massive environmental problems, people have begun to assert themselves. Victories were seen on four continents: in Bolivia a draconian response to protestors embarrassed the government, causing them to drop plans to build a road through Tipnis, an indigenous Amazonian reserve; in Myanmar, a nation not known for bowing to public demands, large protests pushed the government to cancel a massive Chinese hydroelectric project; in Borneo a three-year struggle to stop the construction of a coal plant on the coast of the Coral Triangle ended in victory for activists; in Britain plans to privatize forests created such a public outcry that the government not only pulled back but also apologized; and in the U.S. civil disobedience and massive marches pressured the Obama Administration to delay a decision on the controversial Keystone XL pipeline, which would bring tar sands from Canada to a global market.
Peru's Cocha Cashu biological station changes management
(12/08/2011)
The San Diego Zoo Global Wildlife Conservancy is taking over management of the productive Cocha Cashu field station in Manu National Park, Peru. To date, nearly 600 scientific papers have come out of research conducted at the station, making it among the five most productive research stations in the Amazon and Andes. Located in a part of the Amazon rainforest that has seen little human impact, the station was founded in 1969, four years before Manu National Park was gazetted.
Brazil passes controversial Forest Code reform environmentalists say will be 'a disaster' for the Amazon
(12/06/2011)
The Brazilian Senate tonight passed controversial legislation that will reform the country's 46-year-old Forest Code, which limits how much forest can be cleared on private lands. Environmentalists are calling the move "a disaster" that will reverse Brazil's recent progress in slowing deforestation in the world's largest rainforests.
Amazon rainforest loss in Brazil drops to lowest ever reported
(12/05/2011)
Deforestation in the Brazilian Amazon fell to the lowest level on record between August 2010 and July 2011 according to preliminary data from Brazil's National Institute of Space Research (INPE).
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