A tropical rainforest is a warm-weather, high-precipitation area of trees. While tropical rainforest biomes are of various sizes, the world’s largest tropical rainforest is the Amazon, which stretches over two million square miles (or 550 million hectares). Tropical rainforests are located worldwide—including Hawaii, Brazil, Central America, South America, Central Africa, and Southeast Asia. Almost all of these tropical rainforests run alongside the equator, between the Tropic of Cancer and the Tropic of Capricorn. The equator provides the necessary temperatures (of above 64 degrees) and average rainfall (at least 66 inches per year) for tropical plants and animals to thrive.

A rainforest must feature the following characteristics to be classified as a tropical rainforest:

• Year-round warm weather: Tropical rainforests require a very particular climate to support their warmth-loving plant and animal species. The average monthly temperatures never dip below 64 degrees Fahrenheit in most tropical rainforests throughout the world—even during the winter months.
• High levels of precipitation: Tropical rainforests receive a significant amount of rainfall. An area needs to receive at least 66 inches of rain per year (with no dry season) to qualify as a tropical rainforest. Most tropical rainforests exceed that number, receiving anywhere from 69 to 390 inches of rainfall per year. Some heavily forested areas that do experience a short dry season, such as the Daintree National Park in Queensland, Australia, are classified as “seasonal tropical forests” rather than true tropical rainforests.

Tropical rainforests are a vital part of the Earth’s ecosystem:

1. Biodiversity: Tropical rainforests support many different species of plants and animals—it’s estimated that around half of all known species on earth live in rainforest environments, from orangutans to bromeliads to amphibians. In addition, a rainforest provides four different settings to support its diverse biomass: the forest floor (usually characterized by thick buttress roots covered in nutrient-rich leaf litter), the understory (including all of the space below the high-up branches), the canopy (where birds forage and epiphytes like orchids grow attached to trees), and the emergent layer (where only the tallest trees reach for sunlight above the canopy). Learn more about biodiversity and how it affects the world.

2. Medicine: Tropical rainforests contain hundreds of thousands of plant species—only a percent have been studied for their medicinal purposes. Over time, scientists have used the compounds found in tropical rainforest plants to develop drugs for cancer treatments, migraines, malaria, fevers, and muscular disorders.

3. Water supply: Rainforests are a key component of the Earth’s water cycle (through precipitation and transpiration) and water supply (through freshwater storage). The Amazon Basin alone contains around one-fifth of the planet’s freshwater, though it only covers four percent of the earth’s land surface.

While rainforests are a vital part of our planet’s ecology, they are shrinking because of human activity. Here are some threats that tropical rainforests face:

• Tree collection: Rainforest trees are a valuable resource in tropical rainforests, but various human activities cut these trees down for other uses. Logging operations use timber for flooring and construction; paper industries turn wood into paper pulp; power plants burn trees to generate power. These activities leave vast tracts of rainforest land bare and destroy acres of natural habitat for plants and animals.
• Deforestation: Deforestation (or forest degradation) is a process by which groves of living trees are killed, and the land is converted to non-forest use—for instance, to use the land for other animals or crops. Human activities—most notably cattle ranching and agricultural practices—lead to deforestation on nearly all of Earth’s continents. Deforestation is particularly destructive in tropical rainforests such as the Brazilian Amazon rainforest and many tropical forests throughout Southeast Asia.
• Climate change: As global warming continues to warm the planet, temperatures rise in tropical rainforests, causing rainfall to decrease. Less rain means fewer healthy rainforest plants—during dry spells, plants’ fruit production becomes unstable, and animals can no longer rely on these food sources. If the planet continues its global warming trend, rainforests will become dry enough to be significantly threatened by forest fires. Learn more about the impacts of climate change.

There are two types of rainforests: tropical and temperate. The primary difference between tropical rainforests and temperate rainforests is location, and thus temperature. Tropical rainforests fall between latitudes 23.5 degrees north and 23.5 degrees south, which means they are much warmer, supporting warm-weather species of plants. Temperate rainforests exist much further away from the equator, falling within latitudes of 40 to 60 degrees north and south, which means their temperature remains mild year-round but not warm enough to support the same warm-weather plants.