Green Mountain National Forest

Fall Foliage
Fall leaves in Green Mountain National Forest
Fall leaves in Green Mountain National Forest (James P. Blair/Photodisc/Getty)

Beginning late in September and continuing throughout October, Vermont's forests explode in a sea of vibrant color as the leaves of deciduous trees lose their chlorophyll in preparation for the coming winter.

The first foliage report is not documented. It may have occurred when an Algonquin Shaman asked the spirits why, as summer ended, green leaves changed to red and yellow, purple and gold. The real answer might have forever remained a medicine man's reply from the spirits. In time, however, science discovered the mechanism behind the spirits' magic: photosynthesis and chlorophyll.

Chlorophyll is a green plant pigment. Photosynthesis is a process wherein cells with chlorophyll use the energy of light to synthesize carbohydrates from carbon dioxide and water, which makes plants grow. As fall begins, daylight hours decline, reducing available fuel for photosynthesis. Chlorophyll in the leaves tails off. Green is no longer the dominant color, and the other leaf pigments begin to predominate. In some tree species, carotenoid pigments remain abundant. Those leaves turn yellow or yellowish. If tannins are present, as in beeches and aspens, the leaf may be bright gold or yellow. In other species, especially oaks and maples, a substance called phloem becomes inactive while photosynthesis is still going on, and sugars accumulate. This circumstance is associated with the red or purplish pigments.

This colorful autumn vision of oaks, maples, beeches, apple trees, ash, cherry, and other hardwoods, against a background spiced with evergreen softwoods, was there all along, but chlorophyll green predominated, suppressing it.

Visit the Green Mountain National Forest by car or footpath. Although autumn foliage is better in some years than in others, nature seldom disappoints.

Published: 22 Sep 2009 | Last Updated: 6 Jan 2011
Details mentioned in this article were accurate at the time of publication


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