Wednesday, October 7, 2015

Why Leaves Change Color in the Fall

Have you ever wondered why leaves change color in the fall? There's fascinating science behind the fall color show here in south central Virginia.

Each leaf in a plant is a tiny, highly efficient factory that manufactures food for the plant throughout the spring and summer. Tiny cells called chloroplasts deep within each leaf contain chlorophyll, a chemical that absorbs sunlight. It also lends leaves their green hue. Chlorophyll transforms carbon dioxide and water into sugars and starch that plants use for food.

Leaves contain other chemicals, however. Carotene, the same chemical that gives carrots their orange color, is found in some plants, as well as xanathophyll and other compounds. These exist in smaller amounts than chlorophyll, so when you look at a tree, for instance, during the spring or summer, you simply see green leaves.

As the light begins to dwindle in both duration and intensity, trees shut down their food-making factories in preparation for winter dormancy. Chlorophyll production ceases. As chlorophyll levels drop, you can see the gorgeous orange and yellow hues more easily. Additional chemical changes in the leaves that prepare them to drop from the trees produce anthocyanin, a red pigment. Depending on how these three pigments mix - anthocyanin, xanathophyll and carotene - you see the gorgeous yellow of aspen leaves, the rich purple and crimson of sumac leaves, or the red-browns of the oak.

Special layers of cells that joint the tips of twigs to the branches develops and severs the leaves from the trees when the tree no longer needs its little food factories. Leaves drift to the forest floor or onto your lawn where nature sends bacteria, fungi, and other helpers to break them down into usable compounds that eventually add them back into the soil.

Why do some years seem to produce more brilliant color than others? According to the State University of New York Extension Service, numerous environmental factors affect the brightness, intensity and hues of fall leaves. Low temperatures that hover just above freezing for prolonged periods of time increase the amount of anthocyanin produced in the fall, giving trees a more intense red color. This especially affect maples. Rainy days, as well as overcast days, increase the intensity of all colors, but an early frost can dim them.

I grew up in New York State and thought that only New England could boast beautiful fall foliage. Then I moved to Virginia and wow - was I dazzled by BOTH the spring and fall colors. We truly live in one of the most beautiful states, and indeed, one of the most beautiful parts of Virginia. Enjoy the fall foliage, and think of the tiny miracles sprinkled throughout each leaf the next time one drifts to your feet on a light autumn breeze.

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