Trees are very important to us for many very practical reasons because of the uses to which the wood can be put. [Topic sentence] However, their value in economic terms is nothing compared to their role in helping to regulate the world's climate and providing fertile soil. [Topic point 1 ] The wholesale destruction of trees is a threat to us all because trees support life. [Specific detail A] A single tree can take up 1000-2000 litres of water from the ground every year, releasing most from the leaves as water vapour. [B] This water vapour is then added to water vapour from other sources to form clouds. [C] It eventually returns to the ground in the form of rain or possibly snow. [D:] This ability to move vast quantities of water vapour from one place to another has a significant effect on the regional climate and on local water table levels. [Topic point 2] Another factor is that the ground in a forest acts like an enormous sponge. [Specific detail A] It absorbs rainwater and holds it within the soil, releasing it gradually back into the atmosphere. [B] Where trees have been cut down, the ground is unable to absorb water so easily and it runs off rapidly causing flooding in other areas. [Topic point 3] A further factor is the degree to which most trees add to the fertility of the soil around them. [Specific detail A] Every year millions upon millions of leaves flutter down and rot into the soil, adding to the richness of the soil base in which other plants can grow. [B] Insects thrive within this rich, damp environment and they are themselves a source of food for other animals up the food chain. [C] All of them are threatened when trees are cut down in large numbers.