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

Young environmentalists ‘plant the future’ in Colombia’s Amazon (Jan 24 2022)
- Young people like Felipe “Pipe” Henao in Guaviare, Colombia, are using tree planting and social media to raise awareness and spread the message of protecting and valuing the environment.
- Colombia’s Institute of Hydrology, Meteorology and Environmental Studies (IDEAM) recorded a nationwide deforestation rate of 171,685 hectares (424,242 acres) in 2020, with Guaviare department in the Amazon being one of the worst hit.
- Despite the damage being done, civil society efforts are already showing gains with efforts like Henao’s.
- His organization alone has connected with more than 150 companies and organizations in and around the town of Calamar and more than 1,800 families, and mobilized more than 1,000 young people to volunteer to clean rivers, protect wetlands and plant more than 60,000 trees.

Grounded by conflict and COVID, Colombia’s bird tourism struggles to soar (Jan 14 2022)
- In Colombia, the landmark 2016 peace accords with the FARC heralded hopes of ushering in bird-watching tourism in previously inaccessible, biodiverse regions.
- Birding tourism has unique advantages, including dedicated bird-watchers who will pay good money to go to remote locations.
- But the pandemic, protests, and the persistent perception of insecurity has stymied the country’s bird tourism industry from reaching its full potential.

Brazil’s illegal gold rush is fueling corruption, violent crime and deforestation (Jan 14 2022)
- Once the epicenter of the global trade in gold, illegal mining is once again surging across the Amazon.
- Its extraction and trade is not only fueling corruption, money laundering and criminal violence – it is accelerating deforestation in the world’s largest tropical forest, says Robert Muggah, co-founder of the Igarapé Institute.
- Muggah details a range of challenges facing efforts to rein in the gold mining sector. He says political leadership is critical to make progress on the issue: “Absent political will from the top, however, Brazil’s gold chain will continue to resemble the wild west.”

Tom Lovejoy’s enduring legacy to the planet (Jan 7 2022)
- Conservation biologist Tom Lovejoy died on Christmas day, 2021 at the age of 80.
- Through his innovative ideas, leadership, and advocacy, Lovejoy leaves an enduring legacy to the field of conservation, writes Jeremy Hance.
- “Among career highlights, Lovejoy published one of the first estimates of global extinction rates in 1980; invented the debt-for-nature swap, a massive boon to conservation areas the world over; he helped raise awareness of the plight of rainforests worldwide, and the Amazon in particular, during the 1980s during the peak save-the-rainforest movement; and he was an advisor to the PBS program, NATURE,” Hance writes.
- “Lovejoy’s work lives on, not only through his fragments project in Brazil, but through years of advising and collaborating with other researchers, celebrities and world leaders, including four US presidents, to preserve the ecological integrity of our natural world.”

Mongabay’s 10 hardest-hitting investigations of 2021 (Dec 29 2021)
- Mongabay published numerous deep-dive investigations this year, some of them data-driven and others relying on on-the-ground interviews, to hold companies and governments accountable.
- The investigations ranged from Brazil to China to Nigeria, covering a wide range of issues, from deforestation to workers’ rights and discrimination against Indigenous peoples.
- In this article, Mongabay looks at some of the most impactful investigations from 2021.

Mongabay’s top Amazon stories from 2021 (Dec 29 2021)
- The world’s largest rainforest continued to come under pressure in 2021, due largely to the policies of Brazilian President Jair Bolsonaro.
- Deforestation rates hit a 15-year-high, while fires flared up again, combining to turn Brazil’s portion of the Amazon into a net carbon source for the first time ever.
- The rainforest as a whole remains a net carbon sink, thanks to conservation areas and Indigenous territories, where deforestation rates remained low.
- Indigenous communities continued to be hit by a barrage of outside pressure, from COVID-19 to illegal miners and land grabbers, while community members living in Brazil’s cities dealt with persistent prejudice.

‘Rampant forest destruction’ wracks reserve as cattle ranching advances in Brazilian Amazon (Dec 29 2021)
- The Terra do Meio Ecological Station comprises some 3.37 million hectares in the Brazilian Amazon state of Pará, and is home to hundreds of species – including some that are threatened with extinction.
- But despite its protected status, Terra do Meio has come under growing pressure, with satellite data showing deforestation doubling in 2021.
- Environmentalists say the destruction within Terra do Meio is being driven by illegal loggers, cattle ranchers and land speculators spilling over from the neighboring Área de Proteção Ambiental (APA) Triunfo do Xingu, a sustainable use reserve that has become the most deforested slice of the Brazilian Amazon in recent years.
- Pending legislation could make it even easier to legalize illegitimate land claims, providing hope to land speculators and cattle ranchers that they could soon receive land titles for land they have deforested and occupied illegally.

The year in rainforests 2021 (Dec 29 2021)
- 2021 was a year where tropical forests featured more prominently in global headlines than normal thanks to rising recognition of the role they play in addressing climate change and biodiversity loss.
- Despite speculation in the early months of the pandemic that slowing economic activity might diminish forest clearing, loss of both primary forests and tree cover in the tropics accelerated between 2019 and 2020. We don’t yet know how much forest was cut down in 2021, but early indications like rising deforestation in the Brazilian Amazon suggest that forest loss will be on the high end of the range from the past decade.
- The following is a look at some of the major tropical rainforest storylines from 2021. It is not an exhaustive review.

Tom Lovejoy, prominent conservation biologist, dies at 80 (Dec 25 2021)
- Tom Lovejoy, a prominent and influential conservation biologist who helped catalyze a global movement to save life on Earth as we know it, has died. He was 80.
- Lovejoy was known as a pioneer of modern conservation efforts, a passionate advocate for wildlife and wild places, and a big thinker who proposed daring and innovative ideas.
- Lovejoy is credited with coining the term “biological diversity”, developing the concept of “debt-for-nature” swap programs, and being one of the earliest to sound the alarm about the global extinction crisis.
- “Tom was a beloved icon in the conservation field: a mentor to many, a friend to all,” said conservation biologist and ethnobotanist, Mark Plotkin. “He fought for biodiversity and against climate change through his ideas, writings, projects, initiatives and all he trained and inspired.”

As the Amazon burns, its Indigenous inhabitants choke on the haze (Dec 23 2021)
- Forest fires in the Brazilian Amazon increased this year, with much of the smoke generated concentrating in the state of Acre and disproportionately affecting the health of Indigenous people.
- At the peak of the fires, in July and August, a total of 88,400 hectares (218,400 acres) of land burned, a 20% increase from the 76,400 hectares (188,800 acres) burned in the same period in 2020.
- Recorded cases of respiratory disease increased by almost 8% from June to September 2021 over the previous year, according to data from the Acre state health department.
- Indigenous people, who have lower immunity and a higher incidence of pre-existing medical conditions, are among the most at-risk groups to the smoke pollution, compounded by the ongoing COVID-19 pandemic.

PICTURES OF THE AMAZON RAINFOREST