The Amazon Rainforest: The World's Largest Rainforest

By Rhett A. Butler [Last update Apr 4, 2024]

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

Brazil’s illegal gold miners carve out new Amazon hotspots in conservation units (Dec 20 2024)
- President Luiz Inácio Lula da Silva’s administration reduced the expansion of illegal gold mining in the Brazilian Amazon, but miners keep finding new sites.
- In 15 conservation units, illegal gold miners destroyed 330 hectares (815 acres) in only two months.
- According to experts, gold miners expelled from Indigenous territories may be migrating to conservation units.
- Alliances with narco mafias and the rise in gold prices are obstacles to fighting illegal mining.

Amazon’s Boiling River gives scientists a window into the rainforest’s future (Dec 20 2024)
- Scientists studying Peru’s Boiling River found 11% fewer tree species for every 1°C (1.8°F) increase in temperature, offering insights into how climate change might affect the Amazon Rainforest.
- The research team discovered that hotter areas not only had fewer species overall but were dominated by heat-tolerant trees that typically grow in the warmest parts of South America.
- The study site is protected by Indigenous Asháninka people as sacred land, but the forest still faces threats from nearby deforestation and fires, reflecting broader challenges across the Amazon.
- The Amazon is experiencing climate pressures, with fire-affected areas in the Brazilian Amazon increasing 18-fold in September 2024, covering a combined area nearly the size of the Netherlands.

Most large banks failing to consider Indigenous rights (Dec 19 2024)
- A new report by finance watchdog BankTrack evaluated the policies and practices of 50 major banks and found that most are failing to fully implement adequate safeguards in line with U.N. human rights principles.
- The 2024 report included three new criteria centered around the rights of human rights defenders and Indigenous peoples and the right to a healthy environment; the majority of banks did not explicitly acknowledge environmental rights are human rights and all failed in due diligence around Indigenous peoples’ free, prior and informed consent.
- The report found that small progress has been made in the last two years as banks improve policies and processes for managing human rights.
- The authors say stronger human rights due diligence laws could be a game changer in driving corporate respect for human rights.

New frog species show how geology shapes Amazon’s biodiversity (Dec 19 2024)
- DNA testing of two new-to-science frog species has shown they share a common ancestor — a species that lived 55 million years ago in the mountains of what is today Brazil’s Amazonas state.
- The multidisciplinary study drew together biologists and geologists to map how geological changes in the mountain range shaped not just its geography but also the diversity of species in the region.
- The two endemic species were collected on two separate peaks — Neblina and Imeri — and their discovery has led to further understanding of the origins and evolution of biodiversity in the Amazon.
- Another expedition to the Tulu-Tuloi Range, located 200 kilometers (120 miles) from Imeri, is scheduled for 2025.

High-flying concessions: Clandestine airstrips, coca crops invade Ucayali’s forests (Dec 16 2024)
- An investigation by Mongabay Latam and Earth Genome identified 45 clandestine airstrips in the rainforest in Peru’s Ucayali department.
- Ten of these airstrips, most likely built for narcotrafficking activity, are located inside nine forest logging concessions.
- Peru’s forest and wildlife monitoring agency, OSINFOR, says only four of these logging concessions are still active.
- Complaints made by concession holders to environmental authorities about the airstrips, as well as associated deforestation and coca cultivation, have been shelved.

Illegal timber from Amazon carbon credit projects reached Europe, U.S. (Dec 16 2024)
- Amazon timber from carbon credit projects targeted by the Brazilian Federal Police was sold to companies in Europe and the United States.
- The group is suspected of land-grabbing and laundering timber from Indigenous territories and protected areas.
- Most of the exported timber belongs to the almost-extinct ipê species and was sent to a company in Portugal.
- The group is also suspected of using fake documents to launder cattle raised in illegally deforested areas.

Recycling gold can tackle illegal mining in the Amazon, but is no silver bullet (Dec 13 2024)
- Artisanal and small-scale gold mining in Brazil’s Tapajós River Basin emits 16 metric tons of CO2 per kilo of gold produced, and 2.5 metric tons of mercury annually, a study has found.
- Researchers suggest that recycling gold could dramatically reduce harmful emissions, along with other solutions such as formalizing mining, adopting clean technologies, and improving gold supply chain transparency.
- Economic dependence, mercury accessibility, and a demand for gold sustain small-scale gold mining, while enforcement risks pushing miners into ecologically sensitive areas.
- In November, Brazil launched a federal operation in the Tapajós Basin to expel illegal gold miners from the Munduruku Indigenous Territory, imposing millions of reais in fines to curb the damage caused by gold mining.

Andes glacier melt threatens Amazon’s rivers & intensifies droughts (Dec 11 2024)
- A new study found that Andean tropical glaciers have reached their lowest levels in 11,700 years, with drastic consequences for the Amazon due to the overlap of the two ecosystems.
- The findings come to light as record droughts in the Amazon in 2023 and 2024, exacerbated by climate change, have severely impacted local communities, including food insecurity and lack of access to drinking water.
- The ice loss in the Andes could reduce the water flow to the Amazon rivers by up to 20%.
- Venezuela is on the verge of becoming the first country in modern history to lose all its glaciers.

Narco airstrips beset Indigenous communities in Peruvian Amazon (Dec 9 2024)
- An investigation by Mongabay Latam and Earth Genome identified 45 clandestine airstrips in the rainforest in Peru’s Ucayali department.
- Thirty-one of these airstrips are located in Atalaya province, and of these, 26 are in or near Indigenous communities and reserves.
- These airstrips and the associated expansion of illicit coca cultivation began to increase in Atalaya 10 years ago, mirroring a rise in violence against Ucayali’s Indigenous communities and their leaders.
- Mongabay Latam spent five days exploring the areas most affected by drug trafficking in Atalaya, including the airstrips, and documenting the critical and alarming situation currently faced by communities in the region.

Loggers and carbon projects forge odd partnerships in the Brazilian Amazon (Dec 9 2024)
- Mongabay examined four REDD+ projects in Pará state and found that all were developed in partnership with sawmill owners with a long history of environmental fines.
- The projects were developed by Brazil’s largest carbon credit generator, Carbonext, a company linked to a major fraud involving REDD+ projects and illegal loggers in Amazonas state.
- According to experts, REDD+ projects may have become a new business opportunity for individuals who have profited from deforestation for decades.

‘Bear’s-eye camera’ reveals elusive Andean bear cannibalism and treetop mating (Dec 6 2024)
- Scientists captured the first-ever camera collar footage of wild Andean bears, revealing unprecedented behaviors, including canopy mating and cannibalism.
- The research team, led by Indigenous researcher Ruthmery Pillco Huarcaya, successfully tracked a male bear for four months in Peru’s challenging cloud forest terrain.
- The footage challenges previous assumptions about Andean bears being solitary vegetarians and shows them behaving more like other bear species.
- While the bears face mounting threats from climate change and human conflict, researchers are combining scientific study with community education to protect them.

15 illegal narco-trafficking airstrips found near Peru Indigenous communities (Dec 4 2024)
- With the help of an artificial intelligence visual search algorithm, Mongabay Latam has identified 15 illegal airstrips.
- These airstrips are being used by drug traffickers to transport narcotics produced in the central rainforests of Peru, which are mostly bound for Bolivia.
- A team of journalists visited these areas and saw firsthand the fear gripping local Indigenous residents. Here, people avoid discussing the issue openly, as they struggle to survive amid an economy overshadowed by drug trafficking.

PICTURES OF THE AMAZON RAINFOREST