Tropical Rain Forests: Lush Equatorial Forests

Tropical rain forests occur where temperatures are warm throughout the year and precipitation occurs almost daily. The annual precipitation is typically from 200-450 cm. Much of this precipitation comes from locally recycled water that enters the atmosphere by transpiration of the forest’s own trees.

Of all the biomes, the tropical rain forests are unexcelled in species richness and variety. Hundreds of species of trees can be found within a few square km. Typically, some trees are very tall (some 50 m), but there are many kinds of plants; some, like palm trees remain relatively small (30-40 m); others, like bromeliads and some ferns, grow on trees. Many species of animals occur; mammals tend to live in trees but some are ground dwellers. Insects and other vertebrates are abundant and show a high diversity. Rain forests occur in some of the most remote regions of Earth and remain poorly known; many undiscovered species are believed to exist there.

Except for dead organic matter at the surface, soils tend to be very low in nutrients. Most chemical elements are held in the living vegetation, which has evolved to survive in this environment; otherwise, rainfall would rapidly remove many chemical elements necessary for life.

Unless strong conservation measures are initiated soon, human population growth and industrial expansion in tropical countries may spell the end of tropical rain forests by the end of the middle of the 21^st century. Biologists fear that many rain forest organisms will become extinct before they have even been identified and scientifically described. 

Deserts are dry areas found in both temperate (cold desert) and subtropical or tropical regions (warm desert) where the rainfall is less than 50 cm/yr. Most deserts have a considerable amount of specialized vegetation, as well as specialized vertebrates and invertebrates. Soils often have abundant nutrients but little or no organic matter and need only water to become very productive. Disturbances are common in the form of occasional fires, cold weather, and sudden, infrequent, and intense rains that cause flooding.

The dominant animals of warm deserts are nonmammalian vertebrates (snakes and reptiles). Mammals are usually small, like kangaroo mice of North American deserts.