My favorite time of year is finally here, with its balmy days, cool nights, and eventual forest color display that everyone looks forward to. If you ever wonder why leaves change color, here’s the latest scoop.
From science class you know that a tree leaf is green because it contains a group of pigments known as chlorophyll. These are so abundant during the summer that the green color hides other pigments that are present. Chlorophyll has the important function of catching the sun’s energy and using it to manufacture food and wood. In the food making process the chlorophyll breaks down, but is constantly replaced during the growing season.
When autumn approaches, chlorophyll is replaced at a slower rate and is gradually used up. As the supply of chlorophyll dwindles, the green color slowly fades, exposing other pigments in the leaf cells. One group of these pigments is the carotenoids, which give leaves the colors of yellow, brown, and orange.
The reds and purples that occur in autumn foliage come from another group of pigments called anthocyanins. These develop in late summer when nutrients, especially phosphate, begin to move out of the leaf into the branches. Anthocyanin production is influenced by the amount of light the leaves receive. When autumn days are bright and cool, and the nights chilly but not freezing, the reds and purple colors are very prominent.
Anthocyanin coloration shows up in red maple, oaks, sourwood, sweetgum, dogwood, blackgum, and persimmon. The carotenoids give bright yellow and orange color to the leaves of hickory, ash, sugar maple, poplar, birch, cherry, sycamore, sassafras, and alder. In many leaves both pigments combine to give a fantastic variety of colors.
Though it varies from season to season, peak color in our area usually occurs around the third week of October. How good the colors will be this year is hard to predict, but with the succession of warm, sunny days and cool, not freezing nights we’ve had may help the color display be good. The dry August we had is causing some trees to show color early, like red maple and yellow poplar.