There are many different types of tropical rainforests, which can be found in all parts of the tropics. While they can be categorized by their structure and features, their species vary from continent to continent.

Lowland Rainforests

Tropical rainforests that lie on comparatively dry lowland sites on "normal" tropical red or yellow clay-rich soils have the greatest variety of species and the most complex structures.

These forests have the greatest number of different commercially useful plants and are the main source of rainforest timber.

Other kinds of tropical rainforests also exist in the lowlands, on soils that are either regularly or permanently waterlogged or flooded.

Tropical rainforests forests also grow on limestone soils, over ultrabasic rocks and on sandy soils.

Wet sites are primarily composed of mangrove forests that have developed under the influence of salt water, freshwater seasonal forest and permanent swamp forest.

In Asia and in small areas of northern South America peat swamp forest can be found in where dead plant matter becomes waterlogged and, instead of decaying, accumulates as peat.

Many swamp forest trees have flying buttresses, or stilt roots, and specialized breathing roots that allow the plant parts below the water table to obtain oxygen.

Swamp forests are usually have simpler structures and are home to fewer species than dry land forests.

The wildlife that lives in forests situated on limestone and ultrabasic rocks is capable of tolerating harsh conditions.

For example, limestone sites are prone to periodic desiccation and plants have adapted to withstand this.

Sandy soils are freely draining, poor in nutrients and usually podzolized - they have a hard iron or humus "pan" layer at some depth in their profile).

They support a forest formation known as a heath forest.

Characteristically, this is a dense forest of pole-like trees, in which a considerable amount of direct sunlight is able to penetrate to ground level.

A heath forest lacks emergent trees and has an even canopy top with a grayish-green hue. The average leaf size is smaller than in other lowland forests.

Heath forests are subject to drought because of the coarse, freely draining soil.

Myrmecophytes, or ant plants and, in Asia, pitcher plants are often found in these forests. They can use their unusual methods of feeding to able to supplement the nutrients obtained from the soil. Heath forest areas are drained by tea-hued streams bearing humus in suspension. Their greatest area is in northwest Amazonia, drained by the Rio Negro.

Mountain Rainforests

In the mountains of the humid tropics, the crests of ridges and the upper slopes are clothed by a small-leaved forest of even canopy which is similar to heath forest in both physiognomy and species composition.

Known as the upper montane rainforest, it forms above the level of persistent cloud. The trees, whose crowns are gnarled, are commonly swathed in a dense covering of mosses and liverworts.

Because of the richness of these epiphytes, these forests are also sometimes called mossy forests.

Many ridge crests have periodic droughts.

The upper montane forest gives way to a zone of very short trees known as elfin woodland.

Above, on the highest mountains, lies the subalpine rainforest - a low, scrubby forest with even smaller leaves.

Below the mossy forest, on all but the smallest mountains, lies lower montane rainforest. This is usually sharply bounded, although it merges gradually downward into lowland rainforest.