After every season of green and shade and the delicious sound of leaves rustling in the evening breeze, deciduous trees have one final gift to offer - an explosion of brilliant color.  For an all too brief period each autumn, every country road becomes a painting and every leafy sidewalk or forest path a gallery.

The way leaves change color is, in its own way, no less miraculous, the result of a complex shift in chemistry as a tree prepares itself for its winter dormant period.  Each leaf, no matter how small, is, in actuality, a sophisticated factory for the conversion of sunlight into energy, a process called photosynthesis.  The chemical compounds essential for this conversion are known as chlorophylls. 

It is these chlorophylls which give leaves their green color.  Chlorophylls are constantly used up during photosynthesis and are constantly replaced by the tree during its growth period.

However, as the growing season ends, the transfer into the leaf of chlorophylls and other important chemicals such as phosphates begins to taper off as a thin layer of cork develops at the stem of each leaf where it attaches to the branch.

Chlorophylls, of course, aren't the only chemicals present in the leaf. A second group of chemicals is a set of pigments called carotenoids. Carotenoids are dark orange and yellow in color and are normally masked by the green of the chlorophylls during the spring and summer. However, as the supply of chlorophylls within the leaf begins to dwindle away, the vibrant oranges and yellows of the carotenoids begin to appear.

The blazing reds and purples are produced by yet a third family of chemicals, anthocyanins, which in turn are manufactured as the by-product of sunlight on sugars within the leaf when its supply of phosphates begins to disappear. The production of anthocyanins varies with temperature and sunlight with the most brilliant displays following periods of bright, cool weather.

The great joy of autumn leaves is the way in which these different chemical compounds mix and change over the course of days and sometimes weeks to produce magnificent swirls of light and color. In the fall, trees become visual symphonies with each leaf an instrument in a great and glorious composition. And it's all for free.

 The great joy of autumn leaves is the way in which these different chemical compounds mix and change over the course of days and sometimes weeks to produce magnificent swirls of light and color. In the fall, trees become visual symphonies with each leaf an instrument in a great and glorious composition. And it's all for free.

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