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 km), 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).
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
How the Sahara keeps the Amazon rainforest going
Scientists have just uncovered an incredible link between the world's largest desert (the Sahara) and its largest rainforest (the Amazon). New research published in Geophysical Research Letters theorizes that the Sahara Desert replenishes phosphorus in the Amazon rainforest via vast plumes of desert dust blowing over the Atlantic Ocean.
Researchers propose improvements for Peru's protected areas
In a study published recently in PLOS ONE, researchers examined Peru's network of protected areas. They found that many of these don't exist in the areas most important for preserving the country's biodiversity and addressing its threats, and suggest alternatives to make the system more effective.
One of Brazil’s rarest primates still holds out in single patch of rainforest
For many years, particularly after renowned naturalist Philip Hershkovitz of the Field Museum in Chicago published his valuable taxonomy of Neotropical Primates, Saimiri vanzolinii was considered to be a mere subspecies of the larger Bolivian squirrel monkey (Saimiri boliviensis). Today, it has the distinction of being one of the most range-restricted primates in all of the Neotropics.
Brazil arrests 'Amazon's biggest destroyer'
Authorities in Brazil have arrested a man they claim to be the single biggest deforester in the Amazon, according to a statement issued by IBAMA, Brazil's environmental protection agency.
Rainforest loss increased in the 2000s, concludes new analysis
Loss of tropical forests accelerated roughly 60 percent during the 2000s, argues a paper published in the journal Geophysical Research Letters. The findings contradict previous research suggesting that deforestation slowed since the 1990s. The study is based on a map of 1990 forest cover developed last year by Do-Hyung Kim and colleagues from the University of Maryland. The map, which includes 34 countries that contain 80 percent of the world's tropical forests, enabled the researchers to establish a consistent baseline for tracking forest cover change across regions and countries over time.
Partnering for conservation benefits Tacana people, Bolivian park
Kneeling in a small clearing amid tropical trees, Baldemar Mazaro skillfully arranges a circle of sticks and a noose of cord in the community of San Miguel de Bala. He hands a branch to a tourist and asks her to prod the sticks as if the branch were the nose of an animal snuffling around, looking for food.
Outgoing government wipes hard drives, slowing environmental progress in Peru
Non-profit organizations are working with the regional government of Loreto, in northeastern Peru, to replace documents and data reportedly lost or destroyed before newly-elected officials took office. Some hard disks had been removed from computers. Others had been deleted, password protected, or infected with viruses, according to regional government officials who took office at the beginning of the year.
Dams or indigenous land: the battle over the Munduruku frontier
The Munduruku indigenous tribe have begun to mark out the limits of their land, in an action that could halt the giant São Luiz do Tapajós hydroelectric dam, the apple of the Brazilian government's eye. Although sacred, this land will be flooded if the dam goes ahead. 'We are not leaving,' says the village chief.
Exclusive: Funai confirms that land threatened by dam projects belongs to indigenous tribe
The Brazilian government opposes granting traditional land to the Munduruku people since it would jeopardize seven proposed hydroelectric dams on the Tapajós River. For this reason, a year-old report by Funai that supports the Munduruku claim has not been officially published, but a copy of this report was obtained by the Brazilian publication Publica.
Drones to scan the Amazon rainforest for hidden civilizations
Researchers are planning to use drones equipped with vegetation-penetrating lasers to scan the Amazon rainforest for signs of past civilizations, reports the University of Exeter.
How do parks affect the poor? Jury’s still out, some experts say
In Peru’s vast northeastern region, where roads are scarce and forests abundant, crackdowns on the illegal plundering of timber, fish, and wildlife are sporadic and expensive. To fill the gap, the Peruvian National Park Service and non-profit conservation organizations encourage community groups to patrol their lakes and forests and control fishing and hunting.
Innovating Brazil nuts: a business with roots in the rainforest
Scientist and entrepreneur turn to Brazil nuts to protect Peru's threatened forests. Sofía Rubio was eight years old when she decided she wanted to be a biologist. 'I would skip school to go to the woods with my father or mother,' who did research in what is now the Tambopata National Reserve in the southeastern Peruvian Amazon, she says.
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