Maple trees, like many other deciduous trees, shed their leaves. This adaptation allows them to survive winter. The vibrant display of fall colors and the subsequent leaf drop are part of a complex biological cycle that prepares the tree for a period of dormancy.
Why Maple Leaves Change Color
The green color of maple leaves during spring and summer comes from chlorophyll, a pigment used for photosynthesis. As days shorten and temperatures cool in autumn, the production of chlorophyll slows and stops. The chlorophyll then breaks down, revealing other pigments that were present in the leaves all along but were previously masked by the dominant green.
Yellow and orange hues are due to carotenoid pigments, which are always present in the leaf’s cells. The brilliant reds and purples, characteristic of many maple varieties, come from anthocyanin pigments. These are not present during the growing season but are actively produced in the fall, particularly when sugars become trapped in the leaves due to cooler nights and sunny days. Decreasing daylight and cooler temperatures trigger these chemical changes, creating autumn foliage.
The Process of Leaf Abscission
After the colorful display, maple trees shed their leaves through abscission. At the base of each leaf stem, or petiole, the abscission zone forms. This zone consists of two layers of cells.
One layer, called the separation layer, contains thin-walled cells that weaken and break apart. The second, a protective layer of cork cells, forms on the tree side. This protective layer seals off the leaf from the tree, preventing water loss and the entry of pathogens. The weakening of the separation layer, combined with environmental factors like wind or rain, causes the leaf to detach and fall. This shedding protects the tree from desiccation and disease during dormancy.
How Maple Trees Survive Winter
Once their leaves have fallen, maple trees enter dormancy, a period of reduced metabolic activity. This allows the tree to conserve energy and endure the harsh conditions of winter. During the warmer months, the tree produces sugars through photosynthesis, which are then converted into starches and stored primarily in its roots and trunk.
These stored carbohydrates serve as the tree’s energy reserves throughout the winter. As temperatures drop, maple trees also increase the concentration of sugars in their sap, acting as a natural antifreeze to prevent ice crystals from forming inside their cells and causing damage. By shedding leaves and entering dormancy, the tree minimizes water loss and prepares for renewed growth when spring arrives.