Fall leaf colors – The truth behind why leaves change color
The colors of fall have provided inspiration for song, art, and even folklore.
For example, legend has it that the mythical Jack Frost nips leaves with his fingers, painting them various hues as he moves through the forest.
But what are the facts behind fall, and why are some years' colors more vibrant than others?
Deciduous trees display the most intense fall leaf color, which is caused by a combination of genetics, climate and geography. Their hues can get so bright that at one time, early colonial painters were accused of exaggeration in their vibrant portrayals of New England's fall.
Actually, those bright red and gold colors are also present in spring and summer, but are masked by the green of chlorophyll. Essential for photosynthesis, chlorophyll is in greatest abundance during the growing season.
As days shorten and temperatures drop, the rate of photosynthesis declines and the dominant green chlorophyll starts to decompose, allowing the yellow and orange pigments of carotenoids to be revealed.
Red, blue and purple pigments called anthocyanin also develop, usually with the onset of excess sunlight and dry weather. These compounds allow the tree to recover any last remaining nutrients before the leaves fall and winter moves in.
Why do we see different hues each year?
There is some truth to the old wives’ tale that rainy days wash the color from leaves. Cloudy, rainy days or warm nights really do reduce the intensity of fall colors.
On the other hand, bright, sunny days and cool nights allow photosynthesis to occur, even when chlorophyll levels are declining. The yellow and orange carotenoids become more powerful, and as night temperatures fall they turn into anthocyanins. This enables the red pigment to reach full development, creating the most colorful fall.