Nature Notes

Vol. II August-September 1984 No. 5


The slow quiet days of fall spent at the desk of the Longmire Museum provide little excitement -- except for the activity across the parking lot. Day by day, from late September into mid October, the vine maples have made drastic changes. The leaves have gone from their summer green to various hues of red, yellow, and orange in just a few short weeks. This delightful phenomenon isn't happening just in Longmire or Paradise or West Side Road or even Stevens Canyon, it's going on all over the Temperate Zone forests of North America!

It started gradually, just a few leaves with their edges turning yellow, but with each new day more leaves changed and more colors began to appear. The trees reached the peak of their intensity just a few days ago and already the brightness of their colors has become subdued. Even so, many a visitor stops to take a picture of the striking trees.

What actually is happening inside each of the blazing trees is a complex chemical process. During the summer, in a healthy green leaf, there are three kinds of pigments present, the predominant one being chlorophyll and thus giving the leaf its color. The other two pigments are masked by the intensity of the chlorophyll. Cool, dry days and lessening sunlight trigger the chemical changes that will bring out the hidden pigments. The changes are the tree's preparation for winter when water becomes locked up as snow and frost. Incidentally, frost has no affect on leaf color or intensity. Bright, sunny fall weather is more conducive to colorful leaf displays than frost.

With the coming of the cool, dry shorter days the chlorophyll breaks down into its components which are then stored in the main tree until spring. Fresh sap is cut off from the leaf by the formation of the corky abscission cells at the base of the stem. It is then that the other pigments get a chance to shine. Xanthophyll provides the yellows while carotene gives the oranges and reds.

Anthocyanin is another pigment that provides the blues and purples. It is not present in the leaf during the summer but emerges from sap that has been caught in the leaf after formation of the abscission layer. Tannin, or tannic acid, is a strong astringent that is found in tree bark, bud scales, and cones. This substance gives the rich brown to oak and beech leaves. Tannin does not break down like the other pigments, and it remains in the fallen leaf long after the bright-colored pigments have broken down and faded away.

It is interesting to note that the same kind of chemicals that produce the spectacular fall colors of leaves also give color to the summer flower fields. Not only that, but they are responsible for the colors of oranges, peppers, tomatoes, beets, carrots, etc.

The bright spot of color the vine maples add to the view from the museum is wonderful. Watching the seasons change becomes more interesting and exciting as you realize there is much more to the vivid colors than meets the eye.

Jolane Willford

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