By Steve Roark
Volunteer, Cumberland Gap National Historical Park
The autumn coloration of trees is always looked forward to with anticipation. The presence of numerous tree species (around 125 for us) having brilliant fall foliage is not common planet wide, as the only other places with a similar abundance of foliage colorations is northern China, Korea, and Japan. A common question this time of year is will the colors be good or not? The answer is meteorological.
The amount, duration, and brilliance of autumn colors depends on weather conditions that occur before and during the time chlorophyll in the leaves is declining. If you remember your science class, chlorophyll is the green biomolecule where photosynthesis takes place in plant leaves. Without chlorophyll we would all starve.

Temperature, light, and water supply are the primary factors that influence the amount of carbohydrates (sugars) in the leaves that favor the formation of a red color pigment called anthocyanin, resulting in bright fall colors. Anthocyanin is normally hidden by the green chlorophyll, which breaks down as fall progresses and the hidden bright colors begin to show. Cool but not freezing temperatures favor anthocyanin production, while an early frost and severe drought is more likely to make leaves them turn brown and drop sooner. Sunny days favor red coloration, while the amount of available water in the soil also affects anthocyanin production, with mild drought favoring bright reds. Rainy days occurring near peak coloration will decrease color intensity, and severe summer droughts can delay the onset of fall color and even extend it. Temperature, sunlight, and moisture are highly variable each year, assuring that no two autumns are ever alike.
The best fall foliage occurs when it’s dry during late summer to start the formation of a barrier in the leaf stem (called the abscission layer) to trap sugar in the leaf. Then, to prevent leaves from falling too soon, rain is needed in early fall. An alternation of rain and bright sunshine along with the gradual dropping of temperatures gives the most brilliant colors.
The prediction for 2024 for our area is to have average to slightly below average color due to the August-September drought period we had. Some yellow poplar and dogwoods are showing color early to due to drought and may drop leaves early. Other species may turn later than usual. Peak fall color usually occurs around the last half of October locally, which this year may extend into early November.