Rainforest

A rainforest is a dense forest found in areas with heavy rainfall throughout the year. Rain typically exceeds hundreds of millimetres per month, and humidity remains high for most of the year. The trees are tall, and their canopies overlap substantially, so little sunlight reaches the ground.

Rainforests consist of layers: the emergent layer of the tallest trees, the canopy that forms the roof of leaves, the understory, and the forest floor. Different types of organisms inhabit each layer. These forests contain a large share of terrestrial species, despite occupying a small portion of Earth's total land area.

Types

Two major types are distinguished. Tropical rainforests are located near the equator, for example the Amazon in South America, the Congo basin in Africa, and the islands of Southeast Asia. Temperate rainforests occur on rainy coasts in temperate regions, such as the west coast of North America, Chile, and New Zealand.

Soils and nutrient cycling

Although tropical rainforests support abundant life, their soils are often poor in nutrients. Nutrients are concentrated in living organisms and fallen leaves. When leaves or animals die, fungi and bacteria decompose them rapidly, and trees immediately absorb the nutrients. This explains why soil productivity declines several years after forest clearing for agriculture.

Climate and carbon

Rainforests influence the water cycle. Trees take up water from the soil and release it to the air through their leaves (transpiration), which generates additional rainfall. They also remove carbon dioxide from the atmosphere and store carbon in their biomass, so forest clearing or burning releases this carbon back into the air.

Threats and conservation

The main threats are agricultural expansion and cattle ranching, logging, mining, and new roads that open previously inaccessible areas. Governments and organizations employ protective laws, designated forest reserves, and payment schemes to countries that conserve forests. Indigenous peoples living in rainforests often pursue land rights claims to prevent logging.