The term Rainforest was coined to describe forests that grow in constantly wet conditions. They can occur wherever the annual rainfall is more than 2,000 millimeters (80 inches) and evenly spread throughout the year. Rain forests are found in temperate as well as tropical regions, but the best-known ones occur in a belt around the Equator. Rain Forests can be divided into two broad categories according to altitude – Lowland and Mountain Rain Forest.
The Amazon Rain Forest contains the largest area of tropical forest in the world, covering around 6 million sq kilometers (2.3 million sq. miles)
Lowland Forests are by far the most extensive, but since they are easily accessible, they have suffered the most damage and clearing. They are also the most prolific of all the plant communities in the world. The canopy can reach more than 45 meters (150 feet) in height and consists of many different tree species living close together. A few trees, known as emergent, break through the canopy, often attaining height of 60 meters (200 feet) with straight, unbranched trunks up to 40-50 meters (130-165 feet) in height. Mountain Rain Forests are much smaller in stature, their growth restricted by a combination of low temperatures, unpredictable rainfall and the lack of nutrients at higher altitudes. These stunted forests play a key role in protecting the environment. Without them, soil erosion in highlands and flash floods in lowlands are the damaging consequences.
Another type, Flooded Forest, is found along the banks of rain forests rivers where large areas of lowland forest are inundated. Higher up the Amazon watershed where the Amazon’s tributaries flood for a short time after heavy rains, the flooded forest is called várzea; farther downstream, in the Amazonian lowlands, there is the swamp forest, or “igapó”.
The Amazon Rain Forest contains the largest area of tropical forest in the world, covering around 6 million sq. kilometers (2.3 million sq. miles) in 9 different countries, 60% in Brazil. Biologically, it is the richest and most diverse region in the world containing about 20% of all higher plant species, perhaps the same proportion of bird species and around 10% of the world’s mammals. Each type of tree may support more than 400 insect species.