Autumn's color is a walk, a drive or a click away

Glorious yellow, burnished orange, radiant red: The appearance of a rainbow of color in the area's foliage marks the shortening days and reduced daylight of fall. By happy coincidence, one triggers the other. Each year, as the sunlight retreats, the leaves on deciduous trees show their underlying character. Literally.

Leaves don't actually "turn" a different color in autumn; rather they shed their green cloak. The apparent color-changing process happens as chlorophyll, the chemical responsible for green growth, disappears with reduced daylight. Chlorophyll is the necessary component for photosynthesis, the process by which plants use sunlight to turn water and carbon dioxide into glucose.

The reduced hours of daylight, rather than the prevailing temperature, determine when the leaves start to reveal their fall colors. As the nights get longer, the cells at the juncture of the leaf and stem divide rapidly and start to block the nutrients and moisture from the roots reaching the leaves. Once the food supply is cut off, the leaves' underlying tones of yellow and orange are then revealed. In this process, each leaf changes color individually, which accounts for how a tree may have uneven patches of color. What the viewer is observing is actually the absence of green.

The different colors are determined by the different chemicals inherent in each species. Brown leaves, for example, are the result of tannins in the leaves, and are typical of oaks. The orange of the bigleaf maple represents carotenoids in the system, the same chemical that colors carrots. Xanthophyll, an oxidized derivative of carotene, is responsible for the yellow pigment common to box elder, hickories, ginkgo, black maple, aspen and larch.

Only some of the bright reds and deep purples, typical of red maples, sweet gum and flowering dogwoods, are actually manufactured at this time of year by anthocyanin, which also colors plums and cranberries. Scientists have not solved the riddle of what purpose this process serves in old leaves though it appears to offer some protection from both ultraviolet rays and the frost and enables trees to keep their leaves longer.

The "leaf color flow" along the east coast of the United States actually follows a wave pattern, according to Kim Coder, professor of silvics at the University of Georgia. The wave starts in mid-September in the mountains of New England, first dominated by yellow, followed by a wave of orange, and finally red, all simultaneously moving downward and southward. When the three colors overlap, the effect is the most dramatic.

The best conditions for the brightest colors are when the growing season has ample moisture, thereby creating leaf volume, followed by a late summer that's moderately dry and an autumn with bright, sunny days and cool nights at around 40 degrees. Cloudy weather — which explains Europe's lack of fall splendor — and warm nights have the opposite effect and tend to bring drab colors. Both high winds and early frosts put an early end to the display of fall color.