Why do leaves fall?

The main reason why some trees shed leaves is to conserve water during the winter months. When root activity and water absorption decrease, deciduous trees drop their leaves. This helps them keep water loss at the minimum. Unlike deciduous trees, which lose their leaves all at the same time, evergreen trees, mostly conifers, shed and replace leaves continuously. Before the leaves fall, triggered by changes in temperature and daylight, groups of the soft cells from around the base of the leaf stalk. These cells produce an enzyme which dissolves the stalk cell walls and causes leaf to detach. Discarding their leaves also helps trees dispose of toxic and waste products which accumulate in the leaves before they fall.