Evapo-transpiration from the leaves of tropical rainforest plants and trees helps creates clouds and thus rainfall. Experiments have shown that, where forests have been cleared, rainfall may decline and, without tree cover, the ground becomes hot and dry.

In Amazonia, this has been shown to have 'knock-on' effects, which makes surrounding areas also become drier, and thus vulnerable to destruction. In Africa, the destruction of forests is believed to have caused climate change leading to drought and the failure of crops.

When rain does fall, the shallow top-soil is washed away, causing siltation in streams and rivers. Because the forest is no longer there to trap the water, run-off can also lead to flash floods.

Because there is less rain and less soil, there is little chance of the forest ever recovering. Even where forests are 'selectively logged' (i.e., only a few of the most valuable trees are removed for their timber) the forest still becomes hotter and drier, and much more prone to catastrophic fires. Natural, unlogged rainforests very rarely catch fire.

Thus, selective logging for timber can start a process which leads to irreversible and complete destruction of the forest.

Forests also have an important influence on the world's climate processes - both through their role in the recycling of greenhouse gases and through the exchange of water and energy with the atmosphere.

Tropical forests are particularly important as a carbon store, because of their high biomass, containing on average 50% more carbon than temperate forests.

The destruction of rainforests has a huge impact on both local and global climates.

For a detailed report on the Congo Basin's forests and climate change, read our report Clouds on the Horizon

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