Unlike evergreen trees, deciduous trees -- like oak, hickory, beech and birch -- drop their leaves in autumn. As winter approaches, leaves can actually be a liability to deciduous trees.
Tree growth periods usually end in late June. Buds are set, and the carbohydrates the tree has produced in its leaves are stored in stems, roots and branches instead of the tree using them to fuel new growth. This stored-up energy will sustain a tree until spring arrives and the cycle renews.
Leaves are a tree's food factories. But in winter, if the tree did not drop its leaves, the watery sap inside them would freeze, possibly costing a tree its life. Rather than take that chance, nature allows the tree to shed its leaves and grow new ones the following spring.
Trees respond to diminishing sunlight and cooler temperatures in fall by developing a layer of cells at the base of each leaf that shuts down fluid and nutrient flow to and from the leaf. Chlorophyll begins to dissipate quickly, giving way to fall colors. Eventually, the tree cuts leaves loose to get ready for winter.
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