Why Leaves Change Color
by Michael Stein & James Cadorette

The annual show of fall color in the Hudson Valley is the result of chemical processes in deciduous trees as they transition from summer to winter. Leaves receive their green color from chlorophyll, a chemical that produces sugars and starches by combining sunlight, water, minerals and carbon dioxide: the process known as photosynthesis. Although highly abundant, chlorophyll is rather unstable and breaks down easily.

The yellow pigment carotene and the orange pigment xanthophyll are also found in leaves throughout the season. Carotene and xanthophyll are used to absorb additional energy from the sun and transfer it to chlorophyll. They also serve to protect chlorophyll from damaging ultra violet light.

During spring and summer, chlorophyll masks the colors of the other pigments. However in autumn, as days shorten, photosynthesis slows and chlorophyll begins to break down and become less concentrated. The fading green allows the yellow and orange pigments to finally present themselves.

In preparation for winter, the tree begins sealing off its connection with the leaf, trapping sugars inside the leaf. Such high concentrations of sugar lead to additional chemical processes which produce anthocyanin, which has a red to purplish color. Variations in sunlight, temperature and rainfall greatly affect the amount of anthocyanin created--thus the best fall colors occur when bright, dry days are followed by cool nights.

The awesome beauty that fall provides may have its origins in the individual demise of thousands of leaves, but this process could not be performed with any more dignity. As Albert Camus once wrote, "Autumn is a second spring, when every leaf is a flower." As the colors begin to change this season, take time to enjoy one of nature's many gifts.

—Michael Stein & James Cadorette, Integral Tree and Landscapers, Inc.