Tropical rain forests are home to more species than all other biomes combined. As the name suggests, rain forests get a lot of rain—at least 2 meters of it a year! Tall trees form a dense, leafy covering called a canopy from 50 to 80 meters above the forest floor. In the shade below the canopy, shorter trees and vines form a layer called the understory. Organic matter on the forest floor is recycled and reused so quickly that the soil in most tropical rain forests is not very rich in nutrients.
Abiotic factors hot and wet year-round; thin, nutrient-poor soils subject to erosion
Biotic factors
Plant life: Understory plants compete for sunlight, so most have large leaves that maximize capture of limited light. Tall trees growing in poor shallow soil often have buttress roots for support. Epiphytic plants grow on the branches of tall plants as opposed to soil. This allows epiphytes to take advantage of available sunlight while obtaining nutrients through their host.
Animal life: Animals are active all year. Many animals use camouflage to hide from predators; some can change color to match their surroundings. Animals that live in the canopy have adaptations for climbing, jumping, and/or flight.
Tropical dry forests grow in areas where rainy seasons alternate with dry seasons. In most places, a period of rain is followed by a prolonged period of drought.
Abiotic factors warm year-round; alternating wet and dry seasons; rich soils subject to erosion
Biotic factors
Plant life: Adaptations to survive the dry season include seasonal loss of leaves. A plant that sheds its leaves during a particular season is called deciduous. Some plants also have an extra thick waxy layer on their leaves to reduce water loss, or store water in their tissues.
Animal life: Many animals reduce their need for water by entering long periods of inactivity called estivation. Estivation is similar to hibernation, but typically takes place during a dry season. Other animals, including many birds and primates, move to areas where water is available during the dry season.
This biome receives more seasonal rainfall than deserts but less than tropical dry forests. Grassy areas are spotted with isolated trees and small groves of trees and shrubs. Compacted soils, fairly frequent fires, and the action of large animals—for example, rhinoceroses and elephants—prevent some areas from turning into dry forest.
Abiotic factors warm; seasonal rainfall; compact soils; frequent fires set by lightning
Biotic factors
Plant life: Plant adaptations are similar to those in the tropical dry forest, including waxy leaf coverings and seasonal leaf loss. Some grasses have a high silica content that makes them less appetizing to grazing herbivores. Also, unlike most plants, grasses grow from their bases, not their tips, so they can continue to grow after being grazed.
Animal life: Many animals migrate during the dry season in search of water. Some smaller animals burrow and remain dormant during the dry season.