Rainforests are teeming with life; in fact, they are home to half of the world's plant and animal species, despite covering only 2% of Earth's total surface area. As the name suggests, rainforests are also very wet. They receive more than 70 inches (178 centimeters) of rain each year each, on average.
There are many types of rainforests, but they can be split into two general categories: tropical and temperate. Tropical rainforests are hot, lush forests located close to the equator, while the rarer temperate rainforests are found farther north or south of the equator, near coastal areas, according to the NASA Earth Observatory. All of the biggest rainforests on Earth fall into the former category but we've included the largest temperate rainforest as an honorable mention at the end.
Amazon Rainforest
The Amazon rainforest in South America is, by far, the largest rainforest in the world. It covers about 80% of the Amazon basin, which spans at least 2.3 million square miles (6 million square kilometers), according to the NASA Earth Observatory. That's more than half the size of India, which is 3.8 million square miles (9.8 million square km), and three times bigger than the next-largest rainforest. The Amazon is spread across nine countries in South America, including Brazil, Peru, and Colombia.
According to the World Wide Fund (WWF), the forest includes at least 10% of Earth's total biodiversity, or a variety of plants, animals, and other living things. This includes many species, such as sloths, harpy eagles, Brazil nut trees, and jaguars. Brazil has the largest chunk of the Amazon rainforest, with more than 1.2 million square miles (3.17 million square km) of primary rainforest. These are mature forests that haven't been disturbed in recent times. However, Brazil is also the No. 1 country for forest loss, with a decline of more than 100,000 square miles (260,000 square km) since 2001, according to data from Global Forest Watch, a nonprofit that monitors forests around the world.
Amazon clearing is typically for larger-scale industrial agriculture — for example, for growing animals such as cattle and crops like soy, according to Goldman. Fires contribute to climate change, which causes the forests to become hotter and drier. That makes them more flammable, creating a destructive feedback loop. Since 1978, humans have destroyed about 386,000 square miles (1 million square km) of the Amazon rainforest through deforestation.
The Congo Basin
The Congo Basin rainforest in Central Africa is the second-largest rainforest, spanning more than 780,000 square miles (2 million square km), according to the WWF. The rainforest encompasses six countries in West and Central Africa: Cameroon, Equatorial Guinea, Gabon, the Central African Republic, the Republic of the Congo, and the Democratic Republic of the Congo (DRC). The DRC has more than 383,000 square miles (992,000 square km) of primary rainforest, more than any other country except Brazil, according to Global Forest Watch data.
Gorillas, forest elephants, and thousands of other species call the Congo rainforest home. Many of these species, such as bonobos (paniscus) and Okapia johnstoni, are found nowhere else on Earth. The Congo Basin is threatened by deforestation, primarily for agriculture. In contrast to the industrial agriculture deforestation in the Amazon, the Congo rainforest is typically cut down for smaller-scale agriculture — for example, by subsistence farmers who grow food to feed their families or to supply local markets.
New Guinea Rainforest
The third-largest continuous rainforest in the world is on the island of New Guinea, which is split into two territories: The eastern half is part of Papua New Guinea, and the western half is part of Indonesia, according to the WWF. This island covers about 303,000 square miles (786,000 square km) and is home to at least 5% of the world's plant and animal species, including tree kangaroos and crowned pigeons.
As mentioned, however, after the Amazon rainforest and the Congo Basin, it becomes harder to rank the largest rainforests. Sometimes, it's easier to measure rainforest cover by countries with clearly defined borders, Goldman said. Papua New Guinea, for example, has about 123,000 square miles (318,000 square km) of primary rainforest, according to Global Forest Watch data. The New Guinea rainforest can also be mapped to include the forests of northern Australia as they were once connected; New Guinea and Australia became separated by ocean about 11,700 years ago, according to the Australian government's Geoscience Australia website.
Commercial logging and agriculture are rapidly deforesting New Guinea. The process usually starts with selective logging of commercially valuable timber, with the area then more likely to be converted to industrial plantations to grow crops such as palm oil.
The Sundaland Rainforest
The Sundaland rainforest is the next-biggest rainforest, at about 197,000 square miles (510,000 square km). The rainforest includes the Malay Peninsula on mainland Southeast Asia and the nearby islands of Sumatra, Java, and Borneo. It spans several countries: Indonesia, Malaysia, Brunei, Thailand, and Singapore. (Here's where things get confusing: Indonesia is home to two separate rainforest blocks: Sundaland and the aforementioned New Guinea rainforest. Indonesia has the third-largest primary rainforest cover of any country, with more than 324,000 square miles (840,000 square km), according to Global Forest Watch data.)
The Sundaland rainforest is home to many species including orangutans, Bornean rainbow toads (Ansonia), and corpse flowers (Rafflesia Arnoldi), the world's largest flower. Indonesia's primary rainforest has declined by more than 37,000 square miles (97,000 square km) since 2001, according to Global Forest Watch data. Nonetheless, Goldman considers the country one of the brighter spots when it comes to deforestation.
"Historically, there has been a lot of commercial oil palm plantation establishment or timber extraction," Goldman said. "But as of the past four years, we've seen decreasing primary forest loss in Indonesia and Malaysia." The Indonesian government has been very active in trying to reduce deforestation, especially since the country was badly affected by fires in 2015.
The Mekong River
The Mekong River basin surrounds the Mekong River, which is the longest river in Southeast Asia, at almost 3,000 miles (4,900 km) long, according to the Mekong River Commission. Myanmar is the most forested country in the Mekong River basin region, with about 51,700 square miles (134,000 square km) of primary rainforest within its borders, according to Global Forest Watch data.
The Mekong River contains more than 1,000 freshwater fish species, including endangered species not found anywhere else, such as the Mekong giant catfish (Pangasianodon), according to the WWF. The rainforests around the river contain a variety of other species, from psychedelic rock to tigers (Panthera tigris). Large-scale agriculture is the primary driver of deforestation in the Greater Mekong region, especially the production of sugar rice, rubber, and biofuels, according to a 2015 report by the WWF.
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