By: Steve Roark
Volunteer Interpreter, Cumberland Gap National Historical Park

Fall coloration of trees in our area is always looked forward to. The presence of a large number of trees having brilliant fall foliage is more unusual than you think, as the only other places in the world with a similar abundance of foliage colorations are 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 color depend 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 chemical that makes leaves green and where photosynthesis takes place in plants. Without chlorophyll we would all starve.

Temperature, light and water supply are the primary factors that influence the synthesis of carbohydrates (sugars) that favor anthocyanin formation and bright fall color. Anthocyanin is a red color pigment in the leaf that is normally hidden by the green of the chlorophyll. Cool but not freezing temperatures favor anthocyanin production. Early frost is more likely to kill leaves, making them turn brown and drop sooner. Sunny days favor red coloration. Water supply also affects anthocyanin production, with mild drought favoring bright reds. Rainy days occurring near peak coloration will decrease color intensity. Late summer droughts can delay the onset of fall color by a few weeks. Temperature, sunlight and moisture are highly variable each year, assuring that no two autumns are ever alike.
The best fall foliage occurs when its dry during late summer to initiate 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 September. An mix of heavy rain and bright sunshine along with the gradual dropping temperatures gives the most brilliant colors.
The prediction for Fall 2021 is for colors be good due to plenty of late summer sunny days and decent rainfall. Some rain would be good around mid-October to help keep leaves on the trees longer. Normally peak coloration in our area is the 3rd week of October, but due to climate change it is occurring more around Halloween. There are several websites that give predictions on when tree coloration will peak for various areas.