why do leaves fall?

Every autumn, deciduous trees and shrubs shed their leaves. In some years, leaves are shed earlier than in others. Why does this happen? What determines when leaves fall?

Leaves are organs that enable plants to capture sunlight and turn it into useable energy in the form of sugars and other carbohydrates. In much of North America, however, winter is too cold for these functions, so most plants become dormant.

When winter approaches, our part of Earth receives less sunlight, and the air grows colder, this season is commonly known as “Fall”. When these changes happen, trees prepare for winter. People believe that leaves die on the tree and the wind blows them off the tree. According to Peter Raven, president of the Missouri Botanical Garden and a renowned botanist, “the wind doesn’t simply pull leaves off trees. Trees are more proactive than that. They throw their leaves off.” Deciduous trees have cells in them that act like scissors. These cells build up a thin bumpy line that push the leaf, bit by bit, away from the stem. You can’t see this without a microscope, says Peter Raven. The tree will then seal the spots where the leaves were attached and bunker down for the winter months.