Leaves from all trees produce the sugar essential for tree survival. This sugar is made when carbon dioxide combines with chlorophyll (the pigment that produces the green color), then further blends with oxygen and hydrogen to form dextrose, a form of sugar.
That process, called photosynthesis, favors temperatures of about 70 degrees and diffused sunlight. In July, when the daylight period starts becoming shorter, the tree’s chlorophyll production slows down and the tree’s leaves rely on its reserves to continue the production of sugars.
Once the sugar is depleted, and there are no other pigments in the leaf, the leaf will become colorless. However, there are three other pigments found in leaves: carotene (yellow), tannin (brown) and anthocyanin (red or purple). Small quantities of carotene and tannins are present in leaves all summer but they don’t rear their color until the green chlorophyll is near absent. That is why birch and poplar turn bright yellow and oaks turn brown in the fall.
The production of anthocyanin become prominent with cooler nights and warm, sunny days. Contrary, the cloudier, duller, overcast days reduce the reds and orange pigments.
Maine is well known for spectacular foliage, drawing thousands of “leaf peepers” here each September. Unlike those who travel to see this wonder, residents are fortunate to see this scientific process unfold in the front yard.
Get out and enjoy the view.
Shelby Rousseau, Phillips, for the Rangeley Lakes Heritage Trust staff and Board
Send questions/comments to the editors.
