Why do some trees lose their leaves in winter?

Some trees with broad-bladed leaves lose their leaves in the winter because the trees has a rest period during the cold weather, and the leaves are not needed for the production of food. These trees are called deciduous trees-from the Latin decidere which means to fall. They drop their leaves in temperate or cold climates, but remain evergreen in the tropics.

Most of these trees grow in the deciduous belt of the earth. This is a mild, temperate region where the summers are warm and the winters cool, and rain falls throughout the year. Some also grow in tropical regions, and a few survive in sheltered places in the belt of the coniferous trees.

The fall of the leaves is brought about by the formation of a weak area, called the abscission layer, at the base of the leaf stalk or petiole. Before the leaves fall, the trees takes back some of the food in the leaves. Chemical changes take place. The result is the brilliant autumn colors of the leaves.

Scientists think that the shortening days in autumn have something to do with the formation of the abscission layer. As the hours of daylight lessen a zone of cells across the base of a leaf stalk softens until the leaf falls. A healing layer then forms on the stem and closes the wound. A leaf scar remains, which may be easily noticeable on winter twigs and help in identifying a tree.

In the spring the trees put forth their leaves and the cycle of nourishment begins again.