The Smoky Mountains experience, on average, quite a few weeks of fall colors during the autumn leaf season. The colors travel down the mountains from higher elevations to the lower. The timing of this foliage change is almost impossible to predict with 100% accuracy as it is dependent on so many factors. One of these factors that is constant is elevation. At the higher elevations colors can start to change as soon as the middle of September with the changing colors of the yellow birch, American beech, mountain maple, hobblebush, and pin cherry.
Peak Fall Colors
Fall colors will start to develop above 4,000 feet around early October. These colors can best be seen on drives such as Clingman’s Dome Road and the Foothills Parkway. The peak of the fall colors on mid and lower elevations begin in mid-October and early November. This is the most spectacular display of fall foliage in the park with the turning of such trees as the sugar maple, scarlet oak, sweetgum, red maple, and the hickories.
The yearly display of fall colors brings visitors to the smokies in mass amounts, especially during the final three weeks of the fall display, making autumn both a beautiful and busy time in the Great Smoky Mountains. Certain areas of the park are busier than others. Cades Cove and Newfound Gap Road will experience the longest traffic delays.
Why Do The Leaves Change Color?
Three factors influence autumn leaf color: leaf pigments, length of night, and weather. None of the other environmental influences-temperature, rainfall, food supply, and so on-are as unvarying as the steadily increasing length of night during autumn. As days grow shorter, and nights grow longer and cooler, biochemical processes in the leaf begin to paint the landscape with Nature’s autumn palette.
Where Do Autumn Colors Come From?
A color palette needs pigments, and there are three types that are involved in autumn color:
- Chlorophyll, which gives leaves their basic green color. It is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to manufacture sugars for their food. Trees in the temperate zones store these sugars for their winter dormant period.
- Carotenoids, which produce yellow, orange, and brown colors in such things as corn, carrots, and daffodils, as well as rutabagas, buttercups, and bananas.
- Anthocyanins, which give color to such familiar things as cranberries, red apples, concord grapes, blueberries, cherries, strawberries, and plums. They are water soluble and appear in the watery liquid of leaf cells.
Both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season. Most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells.
During the growing season, chlorophyll is continually being produced and broken down and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed. The carotenoids and anthocyanins that are present in the leaf are then unmasked and show their colors.
Certain colors are characteristic of particular species. Oaks turn red, brown, or russet; hickories, golden bronze; aspen and yellow-poplar, golden yellow; dogwood, purplish red; beech, light tan; and sourwood and black tupelo, crimson. Maples differ species by species-red maple turns brilliant scarlet; sugar maple, orange-red; and black maple, glowing yellow. Striped maple becomes almost colorless. Leaves of some species such as the elms simply shrivel up and fall, exhibiting little color other than drab brown.
The timing of the color change also varies by species. Sourwood in southern forests can become vividly colorful in late summer while all other species are still vigorously green. Oaks put on their colors long after other species have already shed their leaves. These differences in timing among species seem to be genetically inherited, for a particular species at the same latitude will show the same coloration in the cool temperatures of high mountain elevations at about the same time as it does in warmer lowlands.
What Makes The Leaves Fall?
In early autumn, in response to the shortening days and declining intensity of sunlight, leaves begin the processes leading up to their fall. The veins that carry fluids into and out of the leaf gradually close off as a layer of cells forms at the base of each leaf. These clogged veins trap sugars in the leaf and promote production of anthocyanins. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.
What Happens To All Those Fallen Leaves?
Needles and leaves that fall are not wasted. They decompose and restock the soil with nutrients and make up part of the spongy humus layer of the forest floor that absorbs and holds rainfall. Fallen leaves also become food for numerous soil organisms vital to the forest ecosystem.
It is quite easy to see the benefit to the tree of its annual leaf fall, but the advantage to the entire forest is more subtle. It could well be that the forest could no more survive without its annual replenishment from leaves than the individual tree could survive without shedding these leaves. The many beautiful interrelationships in the forest community leave us with myriad fascinating puzzles still to solve.