Why Do the Leaves Change Color?

by Michelle Wallace

Society is profoundly impacted by autumn. Every year as the days get shorter, nights grow longer, and the temperature outdoors becomes cooler the leaves in our abundant deciduous forests across the state and country begin to turn bright hues of gold and crimson. Literally millions of tourists every year come to visit our national and state forests to experience fall’s brilliance. Perhaps the warm colors are nature’s way of warming our spirits in preparation for the cold temperatures that follow.

The changing of color in leaves is largely connected to the change in the length of day. As nights grow longer and days grow shorter, photosynthesis and chlorophyll production in the leaves slows down until it eventually comes to a stop. Chlorophyll in a leaf is what gives leaves their green color. When chlorophyll is absent the other pigments present inside the leaf begin to appear. These pigments are known as caroteniods. They produce colors of yellow, orange, and brown. In addition to the change in the length of day, a plant’s fall color is influenced by the weather and the intensity of light. Anthocyanins pigments (reds and purples) are produced when there are excessive amounts of sugar in the leaves in combination with bright light. It is hypothesized that the anthocyanin pigments in leaves help to protect the photosynthetic system as plants prepare to go dormant and nutrients are being transferred to other areas of the plant. The anthocyanin pigment produced in some leaves is largely dependent on the pH level of the cell sap (sugar) in the leaf. Leaves with highly acidic cell sap produce very red hues while foliage with lower pH levels produce purple hues.

The weather is what causes a corky membrane to develop between the branch and the leaf stem. This membrane reduces the flow of nutrients into the leaves and begins this whole process which is completed when a layer of cells at the base of each leaf is clogged, sealing the tree from the environment and finally causing the leaf to fall off.

Nature creates this magical canvas every fall which is an inspiration to gardeners and outdoor enthusiasts. Consider incorporating a few tree specimens into your landscape that have stunning fall foliage. The United States National Arboretum has a wonderful list of plants listing their fall foliage colors that range from yellow to brilliant red. Go to http://www.usna.usda.gov/PhotoGallery/FallFoliage/FallColorList.html . To find out more information on planting trees and shrubs in North Carolina go to http://www.ces.ncsu.edu/depts/hort/hil/hil-601.html .