Fall is most certainly in the air. Well, at least this week it is! In our area sometimes it's difficult to determine when the coming season will "stick" so to speak. Often the seasons waffle back and forth trying to decide when to get into full swing. Some years we even skip seasons all together, going straight from summer into winter or some such combination.
This year I have a feeling we will be seeing plenty of trees with fall color. Liquidambars, chinese pistache, maples, ginkgo, hackberry, and others should bring many colors into full view.
So why do fall colors happen? The answer has to do with the pigments found in leaves. During most of the year, the pigment (chlorophyll) that gives leaves their green color is dominant. The main way plants make food is through the process of photosynthesis, during which chlorophyll contained in special cells (chloroplasts) teamed with sunlight helps to synthesize food.
The ideal time for the formation of food and chlorophyll is during warm, sunny days. As temperatures begin to drop, food-making wanes and chlorophyll is not replaced. The green color disappears.
Leaves also contain other pigments in their chloroplasts such as carotenoids, anthocyanins and tannins. These pigments are less dominant, and are masked by the green chlorophyll throughout most of the year. Once the chlorophyll breaks down, these other pigments begin to show.
Carotenoids are responsible for yellow to golden colors, anthocyanins for reds, purples and pinks, and the tannins for brown colors. Often a mixture of these pigments also produces color.
photo by Holly Guenther
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