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
Amazon trees super-diverse in chemicals
In the Western Amazon—arguably the world's most biodiverse region—scientists have found that not only is the forest super-rich in species, but also in chemicals. Climbing into the canopy of thousands of trees across 19 different forests in the region—from the lowland Amazon to high Andean cloud forests—the researchers sampled chemical signatures from canopy leaves and were surprised by the levels of diversity uncovered.
Sharp jump in deforestation when Amazon parks lose protected status
Areas that have had their protected status removed or reduced have experienced a sharp increase in forest loss thereafter, finds a new study published by Imazon, a Brazilian NGO.
Is Brazil's epic drought a taste of the future?
With more than 140 cities implementing water rationing, analysts warning of collapsing soy and coffee exports, and reservoirs and rivers running precipitously low, talk about the World Cup in some parts of Brazil has been sidelined by concerns about an epic drought affecting the country's agricultural heartland.
New $20,000 reporting grant explores benefits of Amazonian protected areas
With six Special Reporting Initiatives (SRI) already under way, Mongabay.org is excited to announce a call for applications for its latest journalism grant topic: Amazonian protected areas: benefits for people. The Amazon’s system of protected areas has grown exponentially in the past 25 years. In many South American nations, the mission of protected areas has expanded from biodiversity conservation to improving human welfare. However, given the multiple purposes and diverse management of many protected areas, it is often difficult to measure their effect on human populations.
The making of Amazon Gold: once more unto the breach
When Sarah duPont first visited the Peruvian Amazon rainforest in the summer of 1999, it was a different place than it is today. Oceans of green, tranquil forest, met the eye at every turn. At dawn, her brain struggled to comprehend the onslaught of morning calls and duets of the nearly 600 species of birds resounding under the canopy. Today, the director of the new award-winning film, Amazon Gold, reports that "roads have been built and people have arrived. It has become a new wild west, a place without law. People driven by poverty and the desire for a better life have come, exploiting the sacred ground."
Two kids, one year, from the Amazon to the Arctic: the environmental adventure of a lifetime
The Kraft family—Larry, Lauri, Jamie (age 8), and Jason (age 6)—are on the trip of a lifetime, a round-the-world tour with an environmental focus. Currently in India, the family has already made their way through the Amazon, Vietnam, Costa Rica, Australia, and the Galapagos, among other wild places. Still left on their itinerary: the Arctic. But the trip isn't all fun and games, instead the Kraft's are using the year abroad to learn first hand about global environmental issues and solutions.
Featured video: camera traps catch jaguars, anteaters, and a sloth eating clay in the Amazon rainforest
These are sights that have rarely been seen by human eyes: a stealthy jaguar, a bustling giant armadillo, and, most amazingly, a sloth slurping up clay from the ground. A new compilation of camera trap videos from Yasuni National Park in the Ecuadorean Amazon shows a staggering array of species, many cryptic and rare.
Helping the Amazon's 'Jaguar People' protect their culture and traditional wisdom
Tribes in the Amazon are increasingly exposed to the outside world by choice or circumstance. The fallout of outside contact has rarely been anything less than catastrophic, resulting in untold extinction of hundreds of tribes over the centuries. For ones that survived the devastation of introduced disease and conquest, the process of acculturation transformed once proud cultures into fragmented remnants, their self-sufficiency and social cohesion stripped away, left to struggle in a new world marked by poverty and external dependence
Photos: mass turtle hatching produces over 200,000 babies
Biologists recently documented one of nature's least-known, big events. On the banks of the Purus River in the Brazilian Amazon, researchers witnessed the mass-hatching of an estimated 210,000 giant South American river turtles (Podocnemis expansa). The giant South American river turtle, or Arrau, is the world's largest side-necked turtle and can grow up to 80 centimeters long (nearly three feet).
Drought, fire reducing ability of Amazon rainforest to store carbon
New research published in Nature adds further evidence to the argument that drought and fire are reducing the Amazon's ability to store carbon, raising concerns that Earth's largest rainforest could tip from a carbon sink to a carbon source.
Amazon rainforest does not 'green up' during the dry season
Analysis of satellite imagery has cleared up a controversy over whether the Amazon rainforest 'greens up' during the dry season.
Brazilian soy industry extends deforestation moratorium
Soy traders and producers in the Brazilian Amazon agreed to extend a moratorium on soybeans produced in recently deforested areas for another year, reports Greenpeace.
Amazon news feed.
AMAZON RAINFOREST PICTURE HIGHLIGHTS
NEXT: Amazon rainforest ecology