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Autumn Leaves

Each year the fall foliage phenomena is affected by local weather patterns.  No two color seasons are exactly the same.  In 2004, the peak of the fall color occurred in late October but in 2005, the peak is occurring unusually late, the first two weeks of November. The weather pattern has now settled into a cycle of sunny days and cool nights, just the type of climate to induce the deepest reds in Black Gum, Red Maple, Scarlet and Red Oak, Flowering Dogwood, and other denizens of the autumn woods. 

What Cause the Leaves to Change Color?

Fall color change is triggered by shortening day length. Trees detect the lengthening hours of darkness and release plant growth regulators to initiate leaf abscission. This happens at exactly the same time each year. That is why we can confidently predict that color change will occur during October. But fall colors are influenced by other factors, including soil conditions, tree health and especially fluctuations in the weather. If we could predict the weather with perfect accuracy, we could plan our leaf looking trips with more certainty.

What Colors Will the Leaves Turn?

The actual color a leaf attains in the fall is determined by the health and nutrition of the tree, the amount of sunlight received by the leaf, available moisture, fluctuations in temperature, and reactions to injury, disease or insect attack, among other things. An overriding factor is species of tree, each species having its own genetic palette of potential colors. There are eighty-four species of trees native to the Southern Appalachians. With an alphabet with eighty-four letters nature can compose an infinite variety of October poems.

This yearís October poem will be vibrant and multi-hued. This is due to the nature of the two primary groups of pigments involved in the fall color show. Yellowish carotenes are accessory pigments, present in green leaves throughout the growing season. They absorb the greenish wavelengths of the solar spectrum that are reflected by chlorophyll molecules, and also protect chlorophyll from excessive solar radiation. Carotenes are more stable than chlorophyll and are revealed in the October leaf as chlorophyll molecules are dismantled and reabsorbed by the tree. Last yearís fall color show consisted primarily of yellow and golden carotenoids, and these reliable pigments will once again illuminate the leaves of birches, tulip trees, hickories and others, including the Striped Maple, an understory tree of middle elevations which produces the most delicate and translucent shade of yellow in autumnís palette.

Red leaves, on the other hand, are produced by pigments known as anthocyanins, a group of chemical compounds produced from sugar storage molecules just prior to leaf fall. Anthocyanin production is enhanced by sunlight. Movement of sugar out of leaves is inhibited by cool nighttime temperatures. Hence, a combination of sunny days (which enhance the formation of sugar and anthocyanin in leaves) and cool nights (which inhibit the movement of stored sugar out of leaves) should lead to an abundance of vibrant red leaves in our autumn forests. The combination of red anthocyanin pigments and yellow carotene pigments results in the blazing oranges typically seen in trees such as Sugar Maple, Sassafras and Mountain Maple. All in all, it should be a glorious October.

When Can We Expect the Colors to be at Their Peak?

The earliest peak over the past quarter century has been October 9. Due to an unusually warm fall, this year's peak will be seen during the first two weeks in November which is defintiely on the late side of the range. Hope for a continuation of sunny, calm, and clear days followed by brisk autumn nights, and enjoy this yearís fall color show! 

-- Dan Lazar

Fall Color Identification Guidebooks

Fall Color Finder, C. Ritchie Bell & Anne H. Lindsey

Pocket size identification guide based on typical leaf size, shape and color.  59pp. $5.95. 

Fall Color and Woodland Harvests, C. Ritchie Bell and Anne H. Lindsey

Guide to the most colorful fall leaves and fruits of the eastern forests.  184 pp. $18.95.