In general, tropical evergreen rain forests can be classified into three main types: lowland, montane, and cloud.
Lowland rain forests cover more territory than the other types and include such trees as mahogany. They grow in warm, wet lowland regions, such as the Amazon River basin in Brazil. Because little sunlight can penetrate the thick cover of trees, little vegetation grows on the forest floor. However, undergrowth may be thick near the forest edges, such as where a river cuts through because more sunlight is available. Where the rain forest meets a coastline and produces a swampy area, mangrove forests may form. Mangroves can survive in salty coastal conditions. (For more information about mangroves, see the chapter titled "Wetland.")
Montane, or mountain, rain forests, such as those found in Malaysia, usually grow on mountainsides at altitudes higher than 3,000 feet (914 meters), although this height may vary depending on location. Here the trees are dense, but they have smaller leaves and are generally shorter, and there is little undergrowth. Montane forests may be subdivided into lower montane and upper montane. At higher altitudes (upper montane), the cooler weather is favored by different species of trees, such as pines, myrtles, laurels, and rhododendrons.
Cloud forests, such as those found in Ecuador, also grow on mountains but usually at altitudes higher than 10,500 feet (3,200 meters). Their name comes from the fact that low-lying clouds form around them, shrouding them in mist. The trees, including some species of pines, tend to be stunted and more twisted than those at lower elevations. However, enough light penetrates to encourage extensive growth of creepers and mosses, which cover the ground and the trunks of trees.
Source: "Rain Forest." U·X·L Encyclopedia of Biomes, Vol. 2. U·X·L, Detroit: 2000.