Ask Stewart: Why Do Leaves Turn Different Colors in the Fall?

Hey Stewart,

Why do leaves turn different colors in the fall?

Andy

Hi Andy,

In spring and summer, leaves act as factories that make most of the food the tree needs to grow. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green color. This pigment absorbs sunlight, and the energy is used to transform carbon dioxide and water into carbohydrates, such as sugars and starch.

In the fall, changes in daylight length and temperature stop the leaves’ food-making process. Chlorophyll breaks down, the green color disappears, and yellow and orange colors become visible, giving the leaves their fall splendor.

At the same time, other chemical changes may occur, forming additional colors through the development of red anthocyanin pigments. Some mixtures produce the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange.

The autumn foliage of some trees shows only yellow colors. Others, like many oaks, display mostly browns. These colors result from mixing varying amounts of chlorophyll residue and other pigments in the leaf during the fall season. Sunny autumn days are needed for the brightest color displays, since anthocyanins require light. Overcast days will lead to more yellows and browns.

As the fall colors appear, other changes are taking place. At the point where the leaf stem attaches to the tree, a special layer of cells develops and gradually severs the tissues that support the leaf. At the same time, the tree seals the cut, so that when the leaf is finally blown off by the wind or falls from its own weight, it leaves behind a leaf scar.

Best wishes for a colorful Fall in the valley!

Stewart

Stewart the Squirrel is the mascot of the Front Royal/Warren County Tree Stewards, a volunteer organization formed in 1997 to promote tree health in our community. Stewart answers tree questions in the Royal Examiner twice a month. To learn more about the Tree Stewards, visit treesfrontroyal.org.