A relatively small proportion of the world s land surface has a suitable climate for the continuous growth of plants throughout the year. Such conditions are found only in the equatorial regions of the world between the Tropic of Capricorn and the Tropic of Cancer and it is here that rainforests grow. Where soil moisture is available for growth throughout the year deciduous plants cannot compete with evergreen species. Below the rainforest canopy conditions are the most constant on Earth. Rainforests experience a high steady temperature, rising to at least 30 C each day and rarely cooling to 20 C at night.
Rainforests are generally humid and occur in areas of high rainfall.
Evergreen plants thrive and the great mass of vegetation breaks the force of the downpours and protects the ground from the impact of the rain. Trees make up the scaffolding of the rainforest with the tallest reaching up to 40 metres and weighing over 100 tonnes. The trees have a dense shallow network of roots which absorb the water and nutrients from the thin soil. Spreading buttresses grow on the lower trunks to support the trees. The broad crowns of the main canopy trees form a continuous band and are bound together by large climbing plants and creepers.