CHEMICAL CLOCK UNMASKS TREES' VIBRANT FALL COLORS

All summer they've remained hidden beneath a green cloak. But as fall approaches, the parade of brilliant tree leaf colors will slowly begin its spectacular show across Kentucky.

The fall colors have been in leaves all along, but they were masked by chlorophyl, a green pigment that combines with sunlight to produce food for tree growth. This rebirth of color is caused by fewer hours of daylight, not "Jack Frost." A "chemical clock" activated by shorter days tells trees to shut down chlorophyl production in preparation for winter. So trees use chlorophyl faster than it's produced. This removes the green mask and the brilliant fall color show begins.

Fall color typically peaks in mid-October. Because we in Kentucky have such a diverse climate and soil composition, many tree species common to both northern and southern states grow here. This provides a variety of fall colors for us to enjoy as we walk or drive through state and local parks and national forests. Our nature sanctuaries and arboretums also have many tree species that put on a brilliant fall color show.

Maple, dogwood, black gum, oak and sassafras trees produce various shades of red color. Trees that provide a range of orange and yellow colors include yellow-poplar, birch, hickory, beech and white oak. Since black gum and sumac trees shut down chlorophyl production early, they are the first to reveal fall color. Both change from green to red leaf by leaf. No one leaf seems to be all green or all red at the same time, giving a spotty appearance throughout the trees.

These two trees have characteristics that make them easy to identify. Black gum is one of the few trees that has right-angled branching. This means that the limbs come away from the main stem at a straight 90-degree angle. Other tree species have limbs with some angling. Sumac also is easy to identify because the leaflets growing along the stem resemble teeth on a saw blade from a distance.

Trees do more than give us a spectacular color show. They also make an important contribution to an on-going ecological system. As leaves drop to the ground, announcing winter's approach, minerals previously taken into trees are recycled. The leaves decompose and return nutrients to growing plants and trees and add organic materials to the soil.

Even as these leaves fall, next spring's leaves are wrapped tightly in buds. When these buds unfurl, they will replenish the air by absorbing carbon dioxide and giving off oxygen.