The geography of rain forests varies, depending upon location, and includes landforms, elevation, soil, and water resources.
The terrain over which lowland forests grow features valleys, rolling hills, old river basins, and level areas. Montane forests develop in mountainous regions, as do cloud forests. Tropical mountains tend to be volcanic in origin, and their slopes are often gentle rather than steep and craggy (rugged and uneven).
Rain forests grow at almost all elevations. Cloud forests, for example, form at more than 10,500 feet (3,200 meters) above sea level (the average level of the surface of the sea). However, the greatest share of rain forested area exists at elevations lower than 3,000 feet (914 meters).
Rain forest soils tend to be deep, red in color, and low in nutrients because the vast number of plants quickly absorb its valuable minerals. The most fertile soil is near the surface where decaying vegetation continually enriches the topsoil. For this reason, tree roots are more likely to remain near the surface. In forests where the shade is dense, few smaller plants may grow and the topsoil layer is richer. Where the ground is rocky and not much soil is present, trees may develop stiltlike projections from their trunks that help anchor them to the ground.
Exceptions to the rule of poor rain forest soils are the soils in Indonesia and parts of Central and South America where volcanoes are present. Volcanic ash contains many minerals and adds nutrients to the soil.
In tropical regions, rivers and streams are often the primary water resources. Daily rainfall not only helps maintain them, but can also cause them to flood.
Source: "Rain Forest." U·X·L Encyclopedia of Biomes, Vol. 2. U·X·L, Detroit: 2000.