The Amazon: The World's Largest Rainforest
By Rhett Butler
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.
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.
The World's Largest Rainforests [more]
1. Amazon Basin, South America
2. Congo Basin, Africa
3. Indonesian Archipelago, Southeast Asia
How large is the Amazon rainforest?
The extent of the Amazon depends on the definition. The the Amazon River drains about 6.915 million sq km (2.722 sq mi), or roughly 40 percent of South America, but generally areas outside the basin are included when people speak about "the Amazon." The biogeographic Amazon ranges from 7.76-8.24 million sq km (3-3.2 million sq mi), of which just over 80 percent is forested. For comparison, the land area of the United States (including Alaska and Hawaii) is 9,629,091 square kilometers (3,717,811 sq km).
Nearly two-thirds of the Amazon lies in Brazil.
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
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.
THE AMAZON RAINFOREST
While the Amazon Basin is home to the world's largest tropical rainforest, the region consists of a number of ecosystems ranging from natural savanna to swamps. Even the rainforest itself is highly variable, tree diversity and structure varying depending on soil type, history, drainage, elevation, and other factors. This is discussed at greater length in the rainforest ecology section.
THE CHANGING AMAZON RAINFOREST
The Amazon has a long history of human settlement, but in recent decades the pace of change has accelerated due to an increase in human population, the introduction of mechanized agriculture, and integration of the Amazon region into the global economy. Vast quantities of commodities produced in the Amazon — cattle beef and leather, timber, soy, oil and gas, and minerals, to name a few — are exported today to China, Europe, the U.S., and other countries. This shift has had substantial impacts on the Amazon.
This transition from a remote backwater to a cog in the global economy has resulted in large-scale deforestation and forest degradation in the Amazon — more than 1.4 million hectares of forest have been cleared since the 1970s. An even larger area has been affected by selective logging and forest fires.
Conversion for cattle grazing is the biggest single direct driver of deforestation. In Brazil, more than 60 percent of cleared land ends up as pasture, most of which has low productivity, supporting less than one head per hectare. Across much of the Amazon, the primary objective for cattle ranching is to establish land claims, rather than produce beef or leather. But market-oriented cattle production has nonetheless expanded rapidly during the past decade.
Industrial agricultural production, especially soy farms, has also been an important driver of deforestation since the early 1990s. However since 2006 the Brazil soy industry has had a moratorium on new forest clearing for soy. The moratorium was a direct result of a Greenpeace campaign.
Mining, subsistence agriculture, dams, urban expansion, agricultural fires, and timber plantations also result in significant forest loss in the Amazon. Logging is the primary driver of forest disturbance and studies have shown that logged-over forests — even when selectively harvested — have a much higher likelihood of eventual deforestation. Logging roads grant access to farmers and ranchers to previous inaccessible forest areas.
Deforestation isn't the only reason the Amazon is changing. Global climate change is having major impacts on the Amazon rainforest. Higher temperatures in the tropical Atlantic reduce rainfall across large extents of the Amazon, causing drought and increasing the susceptibility of the rainforest to fire. Computer models suggest that if current rates of warming continue, much of the Amazon could transition from rainforest to savanna, especially in the southern parts of the region. Such a shift could have dramatic economic and ecological impacts, including affecting rainfall that currently feeds regions that generate 70 percent of South America's GDP and triggering enormous carbon emissions from forest die-off. These emissions could further worsen climate change.
PROTECTING THE AMAZON RAINFOREST
While destruction of the Amazon rainforest is ongoing, the overall rate of deforestation rate in the region is slowing, mostly due to to the sharp drop in forest clearing in Brazil since 2004.
Brazil's declining deforestation rate has been attributed to several factors, some of which it controls, some of which it doesn't. Since 2000 Brazil has established the world's largest network of protected areas, the majority of which are located in the Amazon region. Since 2004 the government has also had a deforestation reduction program in place. This includes improved law enforcement, satellite monitoring, and financial incentives for respecting environmental laws. Furthermore, the private sector — especially the soy, logging, and cattle industries — are increasingly responsive to consumer demand for less-damaging commodities. Finally the Brazilian Amazon has been the site of a number of innovative and ambitious conservation experiments, ranging from jurisdictional commodity certification to indigenous led Reducing Emissions from Deforestation and Degradation (REDD+) projects to Norway's billion dollar performance-based payment for cutting deforestation.
RECENT NEWS ON THE AMAZON
Peru eyes the Amazon for one of world’s most powerful dams
Peru is proposing a huge hydroelectric dam in the Amazon that, if built, will be one of the most powerful on Earth, do significant harm to the environment, and flood the homes of thousands of people. The proposed mega-dam would be constructed at the Pongo de Manseriche, a spectacular gorge on the free flowing Marañón River, the main source of the Amazon River.
China’s investment in Latin America taking toll on the environment, setting the stage for conflict
China has been investing heavily in Latin America’s natural resources and crude oil. Recently, the country even pledged to invest $250 billion over the next decade to strengthen its presence in the region, and compete with the U.S. But this increasing Chinese trade and investment in Latin America is also increasing environmental and social conflict, finds a new report published by Boston University.
What's the current deforestation rate in the Amazon rainforest?
Nearly two-thirds of the Amazon rainforest is located in Brazil, making it the biggest component in the region's deforestation rate. Helpfully, Brazil also has the best systems for tracking deforestation, with the government and Imazon, a national civil society organization, releasing updates on a quarterly and monthly basis using MODIS satellite data, respectively. Both the Brazilian government and Imazon release more accurate data on an annual basis using higher resolution Landsat satellite imagery.
Zero deforestation commitments bearing fruit in the Amazon
A high profile pledge by the world's largest meat company to limit deforestation for cattle production in the Amazon appears to be working, resulting in a dramatic increase in compliance with environmental registries and reduced forest clearing among supplier ranches, finds a comprehensive study published in the journal Conservation Letters.
Videos reveal rare birds, wild monkeys, and jaguar family in oil-exploited park
A compilation of new camera trap videos from Yasuni National Park shows off rarely seen species like the rufuos-vented ground cuckoo and the short-eared dog as well as odd behavior, like sloths licking salt from the ground. The compilation is produced by Diego Mosquera, manager and head of the camera trap program at Tiputini Biodiversity Station.
Peru considers fate of Amazon wildlife paradise
The fate of La Sierra del Divisor, a 1.5 million hectare reserve lauded for its megadiversity of wildlife, will soon to be decided. According to El Comercio, next week the Peruvian government is expected to rule whether Divisor will be declared a national park. The designation, which was requested by local groups nearly a decade ago, would strengthen legal protection of the area, which faces logging, mining, coca cultivation, and agricultural encroachment. It would also establish rules for the buffer zone around the potential protected area.
Brazilian Amazon nears deforestation threshold past which wildlife may crash, says study
A study on the impact of forest loss on biodiversity, recently published in the journal Conservation Biology, shows that one-third of the Brazilian Amazon is headed toward or has just passed a threshold of forest cover beyond which species loss accelerates and is more damaging.
Giant Amazonian catfish threatened by dams
Giant catfish are among the most important commercial fishes in the Amazon Basin. A new study suggests that their sensitive life cycle may be interrupted by dams in their last remaining refuge on the Madeira River.
Featured video: the Uncharted Amazon trailer
The up-coming documentary, Uncharted Amazon, promises to highlight both the little-seen wildlife and the people of the Las Piedras River system in the Peruvian Amazon, one of the most remote wildernesses on the planet.
'Deforestation fronts' revealed
Environmental group WWF has released a new report projecting where the organization believes the bulk of global deforestation is likely to occur over the next 15 years. The analysis, published today, highlights eleven regions where 'the bulk of global deforestation is projected to take place' by 2030.
Deforestation in Brazilian Amazon continues to accelerate
Deforestation in the Brazilian Amazon — the planet's largest rainforest — continues to pace well ahead of last year's rate, reveals data released by Imazon, a Manaus-based nonprofit.
Camera traps catch rare Amazon bird following peccaries
Although a large, attractive bird found across Latin America, scientists know almost nothing about the rufous-vented ground cuckoo (Neomorphus geoffroyi). Renzo Piana, the director of science and research with the Amazon Conservation Association, described the bird as "rare," "cryptic," "mainly solitary," and "mostly silent"—much of which explains why so little is known about it.
Amazon news feed.
AMAZON RAINFOREST PICTURE HIGHLIGHTS
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