The Amazon Rainforest: The World's Largest Rainforest

By Rhett A. Butler [Last update June 4, 2020]

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 percent 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 river.

The river system is the lifeline of the forest and its history plays an important part in the development of its rainforests.

WHERE THE AMAZON RANKS AMONG GLOBAL RAINFORESTS

The Amazon is the world's biggest rainforest, larger than the next two largest rainforests — in the Congo Basin and Indonesia — combined.

As of 2020, the Amazon has 526 million hectares of primary forest, which accounts for nearly 84% of the region's 629 million hectares of total tree cover. By comparison, the Congo Basin has around 168 million hectares of primary forest and 288 million hectares of tree cover, while the combined tropical areas of Indonesia, Papua New Guinea, Malaysia, and Australia have 120 million hectares of primary forest and 216 million hectares of tree cover.

THE HISTORY OF THE AMAZON RAINFOREST

At one time Amazon River flowed westward, perhaps as part of a proto-Congo 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 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.

Note: Human populations have shaped the biodiversity of the Amazon. See Amazon people for more.

THE AMAZON RIVER TODAY

Today the Amazon River is the most voluminous river on Earth, carrying more than five times the volume of the Congo or twelve times that of the Mississippi, draining an area nearly the size of the forty-eight contiguous United States. During the high water season, the river's mouth may be 300 miles wide and every day up to 18 billion cubic meters (635 billion cubic feet) of water flow into the Atlantic. That discharge, equivalent to 209,000 cubic meters of water per second (7.3 million cubic feet/sec), could fill over 7.2 million Olympic swimming pools per day or 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's influence on the movement of moisture extends beyond the water that flows down the Amazon river. The trees of the Amazon rainforest pump vast quantities of water vapor into the atmosphere every day via transpiration. While much of this water falls locally as rain, some of this moisture is carried by airflows across other parts of the continent, including the agricultural heartland of South America to the south. This movement has been likened to "flying rivers". By one estimate, 70% of Brazil's gross national product comes from areas that receive rainfall generated by the Amazon rainforest.

THE AMAZON RAINFOREST

While the Amazon Basin is home to the world's largest tropical rainforest, the region consists of myriad other 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 Amazon rainforest ecology section.

AMAZON BIODIVERSITY

The Amazon is home to more species of plants and animals than any other terrestrial ecosystem on the planet -- perhaps 30 percent of the world's species are found there. The following numbers represent a sampling of its astounding levels of biodiversity:

• 40,000 plant species
• 16,000 tree species
• 3,000 fish species
• 1,300 birds
• 430+ mammals
• 1,000+ amphibians
• 400+ reptiles

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., Russia, 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 dropped between the mid-2000s and mid-2010s, mostly due to to the sharp decline in forest clearing in Brazil. However deforestation has been steadily rising in the region in more recent years.

Brazil's decline in its deforestation rate between 2004 and 2012 was attributed to several factors, some of which it controls, some of which it doesn't. Between 2000 and 2010 Brazil established the world's largest network of protected areas, the majority of which are located in the Amazon region. In 2004, the government implemented a deforestation reduction program which included improved law enforcement, satellite monitoring, and the provision of financial incentives for respecting environmental laws. Independent public prosecutors offices played a particularly important role in pursing illegal activities in the Brazilian Amazon. The private sector also got involved, especially after 2006 when major crushers established a moratorium on new deforestation for soy. That soy moratorium was followed by the "Cattle Agreement", which major slaughterhouses and beef processors committed to source cattle only from areas where environmental laws were being respected.

However these conservation initiatives started to break down in the Brazilian Amazon in the mid-2010s. Major cattle producers circumvented the rules through livestock laundering, while financial incentives for conserving forests failed to materialize at the expected scale needed to change landowners' behavior. The Temer and Bolsonaro Administrations dismantled environmental regulations, reduced environmental law enforcement, stripped conservation areas and indigenous territories of protections, and encouraged a wide range of industries (mining, logging, agribusiness) to expand extraction and conversion in the Amazon. In 2019, deforestation in the Brazilian started accelerating rapidly.

THE LATEST AMAZON RAINFOREST NEWS

Lessons from the 2021 Amazon flood (commentary) (23 Jul 2021 16:25:38 +0000)
- In June 2021, the annual flood season in the western and central Amazon reached record levels, and dramatic scenes of inundated homes, crops and city streets captured attention beyond Amazonia. This event provides lessons that must be learned.
- The high flood waters are explained by climatological forces that are expected to strengthen with projected global warming. Damaging floods represent just one of the predicted impacts in Amazônia under a warming climate.
- The administration of Brazilian President Jair Bolsonaro must change its current denialist positions on global warming and its policies that encourage deforestation. The Amazon forest must be maintained for many reasons in addition to its role in avoiding climate change.
- This post is a commentary. The views expressed are those of the author, not necessarily Mongabay.

Amazon and Cerrado deforestation, warming spark record drought in urban Brazil (22 Jul 2021 14:36:56 +0000)
- Southern and central Brazil are in the midst of the worst drought in nearly 100 years, with agribusiness exports of coffee and sugar, and the production of hydroelectric power, at grave risk.
- According to researchers, the drought, now in its second year, likely has two main causes: climate change, which tends to make continental interiors both hotter and drier, and the deforestation of the Amazon rainforest and Cerrado savanna biomes.
- Deforestation has caused the loss of almost half of the Cerrado’s native vegetation, which helps hold vast amounts of water underground, maintaining aquifers that supply the nation’s rivers with water. In the Amazon, rainforest loss is preventing billions of tons of water vapor from reaching the atmosphere.
- President Jair Bolsonaro acknowledges neither climate change nor deforestation as sources of the drought, but attributes it instead to the country and himself being “unlucky.” The administration’s drought response so far is to reactivate fossil-fuel power plants, which pollute heavily and are costly to operate.

Planned Brazil-Peru highway threatens one of Earth’s most biodiverse places (22 Jul 2021 11:54:03 +0000)
- Serra do Divisor National Park on Brazil’s border with Peru is home to numerous endemic animals and more than a thousand plant species, but faces a double threat from a planned highway and a bid to downgrade its protected status.
- The downgrade from national park to “environmental protection area” would paradoxically open up this Andean-Amazon transition region to deforestation, cattle ranching, and mining — activities that are currently prohibited in the park.
- The highway project, meant to give Acre another land route to the Pacific via Peru, has been embraced by the government of President Jair Bolsonaro, which has already taken the first steps toward its construction.
- Indigenous and river community leaders say they have not been consulted about the highway, as required by law, and have not been told about the proposed downgrade of the park, both of which they warn will have negative socioenvironmental impacts.

As soy frenzy grips Brazil, deforestation closes in on Indigenous lands (21 Jul 2021 22:38:09 +0000)
- A large swath of rainforest has been cleared and was burned on the edge of the Wawi Indigenous Territory in the Brazilian Amazon.
- The fire is one of many being set to clear land for soy cultivation, much of it legally mandated, as demand for the crop sees growers push deeper into the rainforest and even into Indigenous and protected areas.
- Enforcement against forest destruction has been undermined at the federal level, thanks to budget cuts and loosened restrictions by the administration of President Jair Bolsonaro.
- The burning threatens to compound health problems in Indigenous communities amid the COVID-19 pandemic, while the use of agrochemicals on the soy plantations poses longer-term hazards.

Protected areas keep adjacent lands safe, but face losing their own protection (21 Jul 2021 16:20:03 +0000)
- Safeguarding nature in one area can displace harmful activities, such as illegal logging or mining, into another, a phenomenon known as leakage or spillover; but how big is the problem?
- The first systematic review of studies examining the effects of protected areas around the globe on their surrounding areas found that less than 12% showed evidence of leakage or spillover, while the majority (54%) reduced deforestation in surrounding areas.
- Another study found that protected areas in the Brazilian Amazon overwhelmingly blocked deforestation in the surrounding forest, again suggesting that protected areas inhibit deforestation both within and outside of their boundaries.
- Experts say environmental and regulatory rollbacks that loosen restrictions on land use, shrink boundaries, or altogether eliminate protections pose a much greater threat to the Amazon than leakage, and efforts should focus on keeping protected areas permanent and improving management and enforcement of regulations.

Hotter and drier: Deforestation and wildfires take a toll on the Amazon (20 Jul 2021 11:41:38 +0000)
- Drought and high temperatures amplify the destructive effects of deforestation and wildfires.
- Across the Amazon Basin, tree species adapted to drier conditions are becoming more prevalent, and in the Central Amazon, savannas have replaced floodplain forests in just a few decades.
- While deforestation remains a main concern, the impacts of forest degradation are becoming increasingly important.

Brazil government faces heat over plan that could underreport forest fires (19 Jul 2021 22:48:56 +0000)
- The Brazilian government faces a new controversy over how it monitors, and ultimately responds to, forest fires, after rolling out a new centralized information system.
- The National Meteorology System (SNM) will collate date from the Brazilian National Institute of Space Research (INPE), the National Institute of Meteorology (INMET) and the Managing and Operational Center of the System to Protect the Amazon (Censipam).
- But the government has sent out mixed messages about how the system will work, raising concerns among scientists and environmentalists that the comprehensive and reliable data sets from INPE will be quashed in favor of underreported deforestation and fire information from INMET.
- The government has sought to allay those fears, saying INPE’s data stream will be maintained, but critics say this isn’t the first time the Bolsonaro administration has tried to undermine INPE for exposing the rising trend in deforestation and fires under the administration.

Brazil’s Amazon is now a carbon source, unprecedented study reveals (14 Jul 2021 22:07:48 +0000)
- According to a study published July 14 in Nature, the Brazilian Amazon is emitting more carbon than it captures.
- This study is the first to use direct atmospheric measurements, across a wide geographic region, collected over nearly a decade that account for background concentrations of atmospheric gases.
- Eastern Amazonia is emitting more carbon than western Amazonia, and southern Amazonia is a net carbon source; Southeastern Amazonia, in particular, switched from being a carbon sink to a carbon source during the study period. The reason: a disruption in the balance of growth and decay and emissions from fires.
- These results have important implications for policy initiatives such as REDD+ that rely on forests to offset carbon emissions: Because different regions of the Amazon differ in their ability to absorb carbon, schemes that use one value for the carbon-capturing ability of the whole Amazon need to be reexamined, scientists say.

Global demand for manganese puts Kayapó Indigenous land under pressure (14 Jul 2021 06:00:51 +0000)
- InfoAmazonia’s Amazônia Minada project has found an unusual rise in demand to mine for manganese last year in Brazil, one of the world’s top producers of the metal.
- Previously, only 1% of mining bids on Indigenous lands were for manganese; in 2020, it was with 15% of all requests, second only to gold.
- Some of the richest manganese deposits in the world are in southeast Pará state, overlapping with the territories of the Kayapó Indigenous people, which have been targeted the most by mining applications in general.
- Demand from Asia, particularly China, has increased the price of manganese, driving illegal mining; 300,000 tons of the ore were seized last year in Brazil, including from a company bidding to mine on Indigenous land.

Armed with data and smartphones, Amazon communities boost fight against deforestation (12 Jul 2021 19:00:23 +0000)
- Equipping Indigenous communities in the Amazon with remote-monitoring technology can reduce illegal deforestation, a new study has found.
- Between 2018 and 2019, researchers implemented technology-based forest-monitoring programs in 36 communities within the Peruvian Amazon.
- Compared with other communities where the program wasn’t implemented, those under the program saw 52% and 21% less deforestation in 2018 and 2019 respectively.
- The gains were concentrated in communities at highest risk of deforestation due to threats like logging and illegal mining.

PICTURES OF THE AMAZON RAINFOREST