Large forests are important to us in many ways. They give us wood for building and heating. They are a home for many kinds of plants and animals. And for many city people, forests are a place to go for a vacation. People can learn about nature there. They can breathe fresh air and sleep in a quiet place. But there is one more reason why forests are important for everyone. The leaves on the treesin a forest help clean the air. Dirty air is a problem in many parts of the world. Without our forests this problem might be much worse.