Equatorial rainforest consists of tall, closely set trees whose crowns form a continuous canopy of foliage and provide dense shade for the ground and lower layers. The trees are characteristically smooth barked and unbranched in the lower two-thirds. Trunks commonly are buttressed at the base by radiating, wall-like roots. Tree leaves are large and evergreen; from this characteristic the equatorial rainforest is often described as broadleaf evergreen forest. Crowns of the trees tend to form into two or three layers, or strata, of which the highest layer consists of scattered emergent crowns rising to 130 ft (40 m) and protruding conspicuously above a second layer, 50 to 100 ft (15 to 30 m), which is continuous. A third, lower layer consists of small, slender trees 15 to 50 ft (5 to 15 m) high with narrow crowns.
Typical of the equatorial rainforest are lianas, thick woody vines supported by the trunks and branches of trees. Some are slender, like ropes, other reach thickness of 8 inch. (20 cm). They rise to heights of the upper tree levels where light is available and may have profusely branched crowns. Lianas may depend upon a growing tree to be carried upward, where the liana has no devices with which to climb by itself. Other woody climbers rise by winding about the tree trunk. Epiphytes are numerous in the equatorial rainforest. These plants are attached to the trunk, branches and foliage of trees and lianas, using the host solely as a means of physical support. Epiphytes are of many plant classes and include ferns, orchids, mosses, and lichens. Some epiphytes are stranglers. These woody vines send down their roots to the soil and may eventually surround the tree, perhaps ultimately replacing it. The Strangling fig (Ficus) is an example. Other stranglers begin as lianas.
A particularly important botanical characteristic of the equatorial rainforest is the large number of species of tress that coexist. It is said that as many as 3000 species may be found in square mile. Individuals of a species are thus widely separated. Consequently, if a particular tree species is to be extracted from the forest for commercial uses, considerable labour is involved in seeking out the tress and transporting them from their isolated positions. Representative trees of the rainforest of the Amazon valley are the Brazilnut (Bertholletia excelsa) and the silk-cotton tree (species of Bombax)
The floor of the equatorial rainforest is usually so densely shaded that plant foliage is sparse close to the ground and gives the forest an open aspect, making it easy to traverse. The ground surface is covered only by a thin litter of leaves. Rapid consumption of dead plant matter by bacterial action results in the absence of humus upon the soil surface and within the soil profile.
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