E+-+Rainforests

Characteristic Features:

Tropical rainforests is distinguished from the vegetation of all other ecosystems by its biodiversity. This term is used to describe the immense number and great variety of living organisms found there. A 100-hectare block of coniferous woodlands may conatin only two or three different types of tree, in the same area in a tropical rainforest there maybe over 500 species of tree, and double this number of flowering species.

Despite the sheer quantity of vegetation present and the way in which climbing plants and creepes run from tree to tree in a chaotic manner, it is possible to recognise five distinctive forest layers. These are shown in the diagram below:



__**Adaptations to climate:**__

The tropical rainforest's bidiversity is a response to climate. There are constant high temperatures, with a mean monthly average above 27 degrees Celsuis, accompanied by high solar light intensity. Rainfall is regular and high, with above 2000mm falling during the year, which creates humid conditions.

Plant communities are fiercely competitive. There is survival of the tallest as the tall trees are drawn upwards by the heat and light, which is why leaf growth is concentrated in the canopy. The leathery upper surfaces of the trees' leaves are necessary to withstand the great power of the sun's rays. The drip tips help the leaves to shed water during the heavy rains.

In the lower layers of the forest, sunlight is in short supply. Ferns are adapted to life on the forest floor by having leaves which intercept a high proportion of the light that reaches there. The shrub layer is sparse because a lack of light, although shrubs quickly take advantage of any gap in the forest canopy.


 * __More plant adaptations:__**
 * trees are branchless and the trunks are tall and thin - this helps them to reach the light from the sun more easily
 * trees are evergreen - this helps them take advantage of the continuous growing season. The can shed their leaves at any time of year
 * leaves often have drip tips - this helps them to shed the heavy rain, and also helps protect them from hungry insects
 * some trees have large buttress roots - these support them in the shallow soil. Others spread their roots over the surface - this helps them capture as many of the available nutrients as possible
 * lianas are woody climbing vines which drape the rainforest. They climb high into the canopy to reach the sunlight, dropping their roots down to the ground
 * epiphytes are plants that grow in the branches of trees - they use the tree for support, not for food


 * __Soils:__**

Soils in tropical rainforests are called latosols. They are generally red or yellowish in colour throughout and do not have distince layers (horizons). The soil is poor in nutirents as most of the nutrients found in the rainforest ecosystem are in the vegetation.

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