Tropical rain forest

The most diverse of all terrestrial biomes, tropical rain forests extend north and south of the equator from 10° N to 10° S. Annual precipitation is commonly more than 250 cm, and tree diversity alone often exceeds 300 species per hectare. Trees grow tall, and many have buttressed roots for support. Lianas and other epiphytic plants are common. Most leaves are evergreen and leathery and many have long pointed tips that facilitate drainage of excess moisture. Because of the high temperatures and heavy rains, decomposition by fungi and bacteria is rapid, preventing the accumulation of organic materials in clay-rich or sandy soils. There are few large grazers, but smaller mammals such as primates, bats, and rodents are highly diverse, as are birds, snakes, and lizards. Insects are especially abundant and diverse. Ants alone make up as much as 30% of animal biomass in rain forests, and they are the principal grazers on rain forest trees.