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

Indigenous communities in Peru ‘living in fear’ due to deforestation, drug trafficking (Dec 2 2022)
- Between 2021 and 2021 the territory of the Indigenous Kakataibo community of Puerto Nuevo lost 15% of its tree cover.
- Satellite data suggest forest loss in the community territory may have accelerated in 2022.
- Residents say outsiders are invading the territory and clearing forest to grow coca crops for the production of cocaine.
- The presence of armed groups is deterring government intervention.

Despite 11% drop in 2022, Amazon deforestation rate has soared under Bolsonaro (Dec 2 2022)
- An area equivalent to the size of Qatar was cleared in the Brazilian Amazon between Aug. 1, 2021, and July 31, 2022, according to data from the country’s National Space Research Institute (INPE).
- Although the figure represents an 11.27% decrease in the Amazon annual deforestation rate compared with the prior year, the government of President Bolsonaro still accounts for the most Amazon destruction in the last 34 years, environmentalists say.
- Bolsonaro’s four-year term ends with a 59.5% boom in Amazon deforestation rates, the highest in a presidential term since 1988, when measurements by satellite imagery began.
- INPE’s report, dated Nov. 3 but only released 27 days later, also triggered criticism among environmentalists, who accused the Bolsonaro’s administration of omitting the annual deforestation data until the end of the UN conference on climate change, COP27, held Nov. 6-20 in Egypt.

2022 Amazon fires tightly tied to recent deforestation, new data show (Nov 22 2022)
- Nearly 1,000 major fires burned in the Amazon during its 2022 fire season, according to the Monitoring of the Andean Amazon Project (MAAP).
- The Brazilian Amazon accounted for the vast majority of the fires, and most burned in recently deforested areas.
- MAAP uses unique satellite data detecting aerosol emissions alongside regular heat alerts, which helps filter out small fires.
- Fires clearing logging debris are linked to soy-driven deforestation in some Brazilian Amazon areas, where many soy-trading companies have not signed zero-deforestation commitments.

In final days before Bolsonaro’s defeat, deforestation boomed in Brazil (Nov 11 2022)
- According to data published today by Brazil’s national space research agency INPE, deforestation in the Brazilian Amazon amounted to 904 square kilometers in October, a 3% increase over last year.
- Year to date, INPE’s deforestation alert system has detected 9,494 square kilometers of forest clearing, 20% more than 2021.
- The figures came less than two weeks after Luiz Inácio Lula da Silva narrowly defeated Jair Bolsonaro in a run off election. Lula, who presided over a sharp drop in Amazon forest deforestation during his terms in office between 2003 and 2010, made saving the Amazon a key part of his bid for the presidency.
- In contrast, Bolsonaro has overseen a steep rise in deforestation, which hit a 15-year high last year.

Mercury rising: Why Bolivia remains South America’s hub for the toxic trade (Nov 8 2022)
- Bolivia is one of the few countries in South America yet to ban the import of the toxic chemical mercury, facilitating its use in illegal mining throughout the region.
- An October U.N. report highlighted Bolivia’s high rate of mercury imports and the need to regulate the distribution and use of the chemical, which has polluted entire watersheds in the country and poisoned animals and Indigenous communities alike.
- Some Bolivian government officials have called for a ban on the import of mercury and better controls on mining operations, many of which run without permits or government oversight.

Why fish are disappearing from Amazonian waters (Oct 27 2022)
- From the coastline to freshwater streams, people living in Amazonia say industrial fishing, deforestation, hydroelectric dams and climate change have reduced fish populations.
- Industrial fishing is one of the main explanations for the low numbers. Fishermen report that large boats are trawling with nets up to 30 kilometers (18.6 miles) in length that do not allow fish to reach the shore.
- Other challenges local fishers are facing have to do with the effects of climate change on rivers and mangroves, including increased temperature and lower pH and oxygen levels in the water, which make it harder for species to survive.
- Hydroelectric dams are a threat to inland Amazonian fish species because they interrupt migratory flow, leading to genetically compromised populations; this phenomenon has been seen in the Xingu River, which, dammed by the Belo Monte hydroelectric plant, is suffering from falling fish reproduction rates.

Amazon community steps in to protect a reserve the government won’t (Oct 19 2022)
- Established in 2018, the Lower Rio Branco-Jauaperi Extractive Reserve still lacks a management plan and the creation of a council with representatives of local communities.
- While the reserve exists on paper, large-scale fish poaching in the Jauaperi River has depleted a key source of food for the area’s traditional communities.
- With laws and court decisions to protect the reserve going largely ignored by the government, a local organization has taken on the task of protecting two iconic and threatened local species: the Amazon turtle and the arapaima.

Beef is still coming from protected areas in the Amazon, study shows (Oct 18 2022)
- According to a new study, 1.1 million cattle were bought directly from protected areas and another 2.2 million spent at least a portion of their lives grazing in protected areas and Indigenous territories.
- Researchers compiled public records on cattle transit, property boundaries and protected area boundaries between 2013 and 2018. The study period ended in 2018 because, “at the start of 2019, this critical information became less available,” the lead author said.
- Under Brazil’s current President Jair Bolsonaro, who was elected at the start of 2019, the country has seen policies weakening various environmental protections and monitoring agencies, and deforestation has reached its highest levels in 15 years.
- Around 70% of deforestation in the Amazon has been linked to cattle ranching. Meat producers have made commitments to stop sourcing from illegally deforested lands, but a lack of information about where cattle are grazing has allowed many companies to escape accountability.

Community study sheds light on wild cat killings in Brazil’s central Amazon (Oct 14 2022)
- Alongside other threats such as deforestation, poaching places wild felids in the Amazon at risk.
- A long-running community-based monitoring program in Brazil’s central Amazonia region identified the number of wild felids killed, motivations for hunting and more.
- Of 71 felids, jaguars were killed the most. Wild cats were predominantly killed opportunistically in flooded forests in areas where human population is highest.

As Brazil starts repaving an Amazon highway, land grabbers get to work (Oct 13 2022)
- Paving work has begun on a stretch of highway running through one of the remotest and best-preserved parts of the Brazilian Amazon — even as questions about the project’s permits abound.
- BR-319 was built in the 1970s to connect the Amazonian cities of Manaus and Porto Velho, but a 405-kilometer (250-mile) “Middle Stretch” fell into disrepair, making the road virtually impassable and killing the flow of traffic.
- Conservation experts have long warned against repaving the Middle Stretch, warning that improved access to this carbon-rich region will lead to a surge in deforestation, burning and land grabbing.
- With the repaving underway, this is already happening, raising concerns about unchecked forest loss that would have massive ramifications for the global climate.

PICTURES OF THE AMAZON RAINFOREST