The commonwealth's forests provide an array of benefits to Virginians and guests. For a brief time each year the forests put on a unique show just for our enjoyment, or so it seems. One might ask “How did all those colors get there? Did they just magically appear?”
This is one of the mysteries of nature that are still not fully understood. It used to be said that Jack Frost visited the mountains and hillsides with his buckets of paints and brushes. Now we know the colors were already there, but hidden beneath the green!
All the complicated reasons why leaves change color are not completely understood. It involves sunlight, moisture, temperature, length of day, chemicals, and hormones. The trees leaves play their version of “hide-N-seek”. A green leaf is green because of the presence of a group of pigments known as chlorophyll. In the growing season of summer the chlorophylls are active. They capture the sun's energy and, using water and carbon dioxide, produce simple sugars. These simple sugars are the tree's food.
During the summer, the chlorophylls are in constant productivity. They are continually breaking down and being used up. During this growing season, however, the plant replenishes the chlorophyll so the leaves stay green. As autumn approaches, the production of chlorophyll slows. Weather plays a role in signaling this change. The green begins to fade as the masking effect disappears. The leaves begin to lose the game of “hide-N-seek.”
Other colors which have been in the leaf all along begin show through. The pigments which give us yellow, brown, and orange are called carotenoids. The reds and purples are called anthocyanins. The anthocyanins are not present in the leaf throughout the growing season as are the carotenoids. They develop in late summer in the sap of the cells of the leaf. The production of the anthocyanins pigments is partly due to phosphates and other chemicals and nutrients moving out of the leaf and into the stem of the plant. The brighter the light during this critical period, the greater the production of these pigments and the more brilliant color displays you see.
Different species of trees change color as the season advances. You begin to see the first signal of leaf change in the fall with spots of red in the forest in early September. These are the black gums changing color. They are followed quickly by the black walnut (yellow) and the dogwood (red). Soon the hickory begins to change to a deep yellow. By mid-October there is a rush of color which some refer to as the “peak season.” There are the brilliant oranges and reds of the sugar maples, red and yellow hues of the red maple, and ranges of colors of the oaks and other species. Finally, toward the end of the season the last show of color is provided by the yellow poplar. By early November the forest is generally shades of browns and bronzes with remaining color spots here and there. Note that when the first winter storm takes the leaves to the forest floor, the leaves of the American beech will hang on, and provide a contrast of gray and light brown in the mature forest. Spring will then be only a few months away. The yellow poplar, the last to turn yellow in the fall, will provide the first tinge of green in the early spring.
More information from the Virginia State Climatology Office.