Rainforest

A rainforest is a forested biome with high annual rainfall due to the Intertropical convergence zone. Some cite a minimum normal annual rainfall of 2000 mm (about 100 inches or 200 centimetres), with normal rainfall at least 60 mm during each of the twelve months of the year. Others set the minimum annual rainfall barrier as low as 1700 mm (about 67 inches). The soil can be poor because high rainfall tends to leach out soluble nutrients. This type of biome is found in both temperate and tropical climates. As well as prodigious rainfall, many rainforests are characterised by a high number of resident species and tremendous biodiversity.

Trees

There are several common characteristics of tropical trees. Tropical species frequently possess one or more of the following attributes not commonly seen in trees of higher latitudes.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Many species have broad, woody flanges (buttresses) at the base of the trunk. Originally believed to help support the tree, now it is believed that the buttresses channel stem flow and its dissolved nutrients to the roots.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Large leaves are common among trees of the C layer. Young individuals of trees destined for the B and A layers may also have large leaves. When they reach the canopy new leaves will be smaller. The large leaf surface helps intercept light in the sun-dappled lower strata of the forest. Drip tips facilitate drainage of precipitation off the leaf to promote transpiration. They occur in the lower layers and among the saplings of species of the emergent layer (A layer).

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Trees are often well connected in the canopy layer especially by the growth of woody climbers or lianas. Plants with epiphytic adaptations, allowing them to grow on top of existing trees in the competition for sunlight.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Other characteristics that distinguish tropical species of trees from those of temperate forests include:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Exceptionally thin bark, often only 1-2 mm thick. Usually very smooth, although sometimes armed with spines or thorns.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Cauliflory, the development of flowers (and hence fruits) directly from the trunk, rather than at the tips of branches.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Large fleshy fruits attract birds, mammals, and even fish as dispersal agents.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~