Rainforests are found all over the world — in West and Central Africa, South and Central America, Indonesia, Southeast Asia and Australia — on every continent except Antarctica. They are vitally important, producing most of the oxygen we breathe and providing habitat for half of the planet's flora and fauna.
Types of rainforests
The term "rainforest" has a wide classification. Typically, rainforests are lush, humid, hot stretches of land covered in tall, broadleaf evergreen trees, usually found around the equator. These areas usually get rain year-round, typically more than 70 inches (1,800 millimeters) a year, according to the Encyclopedia Britannica. Various types of forests, such as monsoon forests, mangrove forests and temperate forests, can be considered rainforests. Here's what makes them different:
- Temperate rainforests consist of coniferous or broadleaf trees and are found in the temperate zones. They are identified as rainforests by the large amount of rain they receive.
- Mangrove rainforests are, like their name, made of mangrove trees. These trees grow only in brackish waters where rivers meet the ocean.
- Monsoon rainforests are also called "dry rainforests" because they have a dry season. These get around 31 to 71 inches (800 mm to 1,800 mm) of rain. Up to 75 percent of the trees in dry rainforests can be deciduous.
Most rainforests are very warm, with an average temperature of 86 degrees Fahrenheit (30 degrees Celsius) during the day and 68 degrees F (20 degrees C) at night.
A rainforest consists of two major areas. The very top part is called the canopy, which can be as tall as 98 feet to 164 feet (30 to 50 meters). This area is comprised of the tops of trees and vines. The rest, below the canopy, is called the understory. This can include ferns, flowers, vines, tree trunks and dead leaves.
Some animals stay in the canopy and rarely ever come down to the ground. Some of these animals include monkeys, flying squirrels and sharp-clawed woodpeckers, according to the Encyclopedia Britannica. [Related: Explore the Amazon Rainforest with New Virtual-Reality Film]
Animals and plants
The rainforest is home to many plants and animals. According to The Nature Conservancy, a 4-square-mile (2,560 acres) area of rainforest contains as many as 1,500 flowering plants, 750 species of trees, 400 species of birds and 150 species of butterflies. The Amazon rainforest alone contains around 10 percent of the world's known species.
Just about every type of animal lives in rainforests. In fact, though rainforests cover less than 2 percent of Earth's total surface area, they are home to 50 percent of Earth's plants and animals, according to The Nature Conservancy. For example, rhinoceroses, deer, leopards, gorillas, chimpanzees, elephants, armadillos and even bears can be found living in rainforests across the world.
Many unusual animals and plants have been discovered in rainforests. For example, the fairy lantern parasite (Thismia neptunis) reappeared in the rainforest of Borneo, Malaysia, in 2018, 151 years after it was first documented. This plant sucks on underground fungi and doesn't need sunlight to survive. "To our knowledge, it is only the second finding of the species in total," the Czech team of researchers wrote in a paper, which was published Feb. 21, 2018, in the journal Phytotaxa.
Some of the animals are also unusual. For example, the tapir is a mammal that looks like a mix between an anteater and a pig and can be found in the rainforests of South America and Asia. The stunning silverback gorilla lives in the rainforest of the Central African Republic. Forest giraffes, or okapi, a strange-looking cross between a horse and a zebra, also inhabit the African rainforest.
One particularly surprising rainforest find is a spider as big as a puppy. The massive South American Goliath birdeater (Theraphosa blondi) is the world's largest spider, according to Guinness World Records. Each leg can reach up to 1 foot (30 centimeters) long, and it can weigh up to 6 ounces (170 grams). [Goliath Encounter: Puppy-Sized Spider Surprises Scientist in Rainforest]
Seventy percent of the plants identified by the U.S. National Cancer Institute as useful in the treatment of cancer are found only in rainforests, according to The Nature Conservancy. Scientists have identified more than 2,000 tropical forest plants as having anti-cancer properties. However, less than 1 percent of tropical rainforest species have been analyzed for their medicinal value.
Humans and animals rely on the rainforest to make the majority of Earth's oxygen. One tree produces nearly 260 lbs. of oxygen each year, according to the Growing Air Foundation, and 1 hectare (2.47 acres) of rainforest may contain over 750 types of trees.
A tree uses carbon dioxide to grow. A living tree draws in and stores twice as much carbon dioxide than a fallen tree releases. But when the tree is cut down, it releases its stored carbon dioxide. For example, dead Amazonian trees emit an estimated 1.9 billion tons (1.7 billion metric tons) of carbon dioxide into the atmosphere each year, according to a study published in the journal Nature Communications in 2014. The same trees typically absorb about 2.2 billion tons (2 billion metric tons) of carbon dioxide. Carbon dioxide makes up around 82.2 percent of all U.S. greenhouse gas, according to the Environmental Protection Agency (EPA).
Out of the 6 million square miles (15 million square kilometers) of tropical rainforest that once existed worldwide, only 2.4 million square miles (6 million square km) remain, and only 50 percent, or 75 million square acres (30 million hectares), of temperate rainforests still exists, according to The Nature Conservancy. Ranching, mining, logging and agriculture are the main reasons for forest loss. Between 2000 and 2012, more than 720,000 square miles (2 million square km) of forests around the world were cut down — an area about the size of all the states east of the Mississippi River.
Deforestation around the world also decreases the global flow of water vapor from land by 4 percent, according to an article published by the journal National Academy of Sciences. Water constantly cycles through the atmosphere. It evaporates from the surface and rises, condensing into clouds. It is blown by the wind, and then falls back to Earth as rain or snow. In addition, water vapor is the most important greenhouse gas in the atmosphere, according to NASA. Even a slight change in the flow of water vapor can disrupt weather patterns and climates.
"Rainforests are under increasing threats for many reasons, including logging, clearing for crops or cattle, and conversion to commercial palm oil plantations," Jonathan Losos, director of the Living Earth Collaborative and William H. Danforth Distinguished University Professor for the Department of Biology, at Washington University in St. Louis, told Live Science. "On top of that, the changing climate is having adverse effects on rainforest health. Last year was an especially bad one for the Amazon, with a substantial uptick in the rate of deforestation."
On the other hand, Losos said, there are some glimmers of hope:
- The two countries with the largest amount of rainforest – Indonesia and Brazil – have both acknowledged the importance of these forests and have taken innovative and aggressive efforts to halt deforestation.
- There is a growing understanding that halting deforestation and reducing carbon dioxide (CO2) emissions are closely linked; new, large-scale efforts are under way to address both concerns.
- While there is a continued decline in primary rainforests, a bright spot is the fact that in many tropical countries, there is an extensive regeneration of secondary forests, which are critical to supporting much of these countries' biodiversity.