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

Why the Amazon’s small streams have a major impact on its grand rivers (Jan 18 2024)
- An unprecedented time-series study in the basin of the Tapajós River, a major tributary of the Amazon, assesses the level of degradation of small rivers threatened by agribusiness expansion.
- Researchers from several universities will assess the conservation status of 100 streams spread between the municipalities of Santarém and Paragominas, at the confluence of the Tapajós and the Amazon, which were first analyzed in 2010.
- The impact of dirt roads and their network of river crossings, which causes sediment load, siltation, erosion and changes in water quality, was one of the factors that caught researchers’ attention in the initial time-series study.
- Experts say that local development models should ideally start from water to land, rather than the other way around, given the importance of water for the rainforest, its biodiversity, and the inhabitants who depend on both.

Amazonia in flames: Unlearned lessons from the 2023 Manaus smoke crisis (commentary) (Jan 17 2024)
- In 2023 the city of Manaus, in central Amazonia, found itself covered in dense smoke from burning rainforest, with levels of toxic PM 2.5 particulates even higher than those experienced that year during the pollution crisis in New Delhi, India.
- The governor of Brazil’s state of Amazonas, where Manaus is located, blamed the neighboring state of Pará for the smoke, a politically convenient theory we show to be false.
- The fires responsible for the smoke were south of Manaus in an area of Amazonas impacted by the notorious BR-319 highway, where a proposed “reconstruction” project would have disastrous environmental consequences by opening vast areas of rainforest to the entry of deforesters.The BR-319 highway project is a top priority for politicians in Amazonas, who take pains not to admit to the project’s impacts. The project’s environmental license is not yet approved, and the Manaus smoke crisis should serve as a warning as to how serious those impacts would be.
- This text is a commentary and does not necessarily reflect the views of Mongabay.

2024 outlook for rainforests (Jan 3 2024)
- Last week, Mongabay published a recap of the major trends in the world’s tropical rainforests for 2023.
- Here’s a brief look at some of the key issues to monitor in 2024.
- These include: Brazil, elections in DRC and Indonesia, forest carbon markets, el Niño, global inflation and commodity prices, advancements in forest data, and progress on high level commitments.

The year in rainforests: 2023 (Dec 29 2023)
- The following is Mongabay’s annual recap of major tropical rainforest storylines.
- While the data is still preliminary, it appears that deforestation declined across the tropics as a whole in 2023 due to developments in the Amazon, which has more than half the world’s remaining primary tropical forests.
- Some of the other big storylines for the year: Lula prioritizes the Amazon; droughts in the Amazon and Indonsia; Indonesia holds the line on deforestation despite el Niño; regulation on imports of forest-risk commodities; an eventful year in the forest carbon market; rainforests and Indigenous peoples; and rampant illegality.

Company sells Indigenous land in Amazonas as NFTs without community’s knowledge (Dec 26 2023)
- Areas of the Apurinã territory in the Lower Seruini area, in southern Amazonas state, were sold by Nemus under an NFT project that promises to preserve the forest and generate carbon credits.
- Brazil’s Federal Prosecution Service recommended suspending the project in December 2022, but a story by InfoAmazonia showed that negotiations continue on the internet; plots in an Indigenous land with its demarcation process underway are traded as NFTs for $17-603.
- Indigenous communities were not properly consulted about the company’s plans and are now calling for government action.
- Nemus told prosecutors that the area was not on “a properly demarcated Indigenous land” and therefore the company understood that “no article of ILO 169 convention on consultation applies.”

Colombian companies defy laws, push Amazon carbon projects in Indigenous lands (Dec 22 2023)
- The promise of an Indigenous university persuaded leaders from the Upper Solimões Indigenous lands, in the Brazilian Amazonas state, to sign carbon contracts with Colombian companies.
- FUNAI, the Indigenous affairs agency, denied authorization for projects in Indigenous lands and advised against signing contracts; the process did not include prior consultation as provided for in ILO Convention 169, of which Brazil is a signatory.
- Indigenous people have not been aware of FUNAI’s guidelines and say they believe there will be classes at the university next year.
- FUNAI and Brazil’s Ministry of Education are not aware of a university project funded with money from carbon credits and say that contracts could be considered null and void.

Detailed NASA analysis finds Earth and Amazon in deep climate trouble (Dec 21 2023)
- A NASA study analyzed the future action of six climate variables in all the world’s regions — air temperature, precipitation, relative humidity, short- and long wave solar radiation and wind speed — if Earth’s average temperature reaches 2° Celsius (3.6° Fahrenheit) above preindustrial levels, which could occur by 2040 if emissions keep rising at current rates.
- The authors used advanced statistical techniques to downscale climate models at a resolution eight times greater than most previous models. This allows for identification of climate variations on a daily basis across the world, something essential since climate impacts unfold gradually, rather than as upheavals.
- The study found that the Amazon will be the area with the greatest reduction in relative humidity. An analysis by the Brazilian space agency INPE showed that some parts of this rainforest biome have already reached maximum temperatures of more than 3°C (5.4°F) over 1960 levels.
- Regardless of warnings from science and Indigenous peoples of the existential threat posed by climate change, the world’s largest fossil fuel producers, largely with government consent, plan to further expand fossil fuel exploration, says a U.N. report. That’s despite a COP28 climate summit deal “transitioning away from fossil fuels.”

Race to destroy the Amazon forest: Brazil’s National Congress set to force construction of Highway BR-319 (commentary) (Dec 20 2023)
- Highway BR-319 and planned connecting roads would bring deforesters to much of what remains of Brazil’s Amazon forest. BR-319 would connect the notorious “arc of deforestation” in southern Amazonia to Manaus, in central Amazonia.
- From Manaus, existing roads would provide access to northern Amazonia, while roads planned to branch off BR-319 would open the western half of Brazil’s State of Amazonas to deforestation. BR-319 is now on a fast track for approval by Brazil’s ruralist-controlled National Congress.
- The proposed law interferes with decisions to be made by Brazil’s licensing system and by the Amazon Fund. While these are not in purview of the National Congress, such things can happen in practice in Brazil.
- An earlier version of this text was published in Portuguese by Amazônia Real. This is a commentary and does not necessarily reflect the views of Mongabay.

Brazil’s “End-of-the-World” auction for oil and gas drilling (commentary) (Dec 16 2023)
- Brazil’s massive 13 December 2023 auction of oil and gas drilling rights betrays a glaring hypocrisy in view of the country’s discourse on climate change. The fossil fuels to be extracted would be a climate-change “bomb”. They also signal no intent to end extraction soon.
- The auctioned areas impact Indigenous and other traditional peoples, Amazonian protected areas for biodiversity, coral reefs and marine biodiversity hotspots. Areas still “under study” for future auctions include the vital Trans-Purus rainforest area in Brazil’s state of Amazonas.
- Brazil’s President Lula needs to control his anti-environmental ministers and replace some of them, such as the minister of mines and energy.
- An earlier version of this text was published in Portuguese by Amazônia Real. This is a commentary and does not necessarily reflect the views of Mongabay.

Major soy producers announce improved deforestation commitments—with caveats (Dec 15 2023)
- Eight soy producers published a statement last week committing to halting deforestation in the Amazon, Cerrado and Chaco biomes by 2025 and the conversion of “non-forest primary native vegetation” by 2030.
- The companies include ADM, Amaggi, Bunge, Cargill, COFCO, LDC, Olam Agri and Viterra.
- Conservation groups have pointed out that without an immediate ban on deforestation, the new commitments would allow soy producers to continue clearing forests in years to come.

PICTURES OF THE AMAZON RAINFOREST