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Hot, dry weather may provide later and less vibrant foliage

By Jill Penley
Freelance Writers

The end of September is when East Tennessee typically starts enjoying autumn colors before a mid-October peak; however, fall foliage prognosticators fear as unusually hot and especially dry weather continues, leaves might begin to turn brown and fall off before displaying the colors we have come accustomed to enjoying in East Tennessee and beyond.
“In all likelihood, our fall foliage colors will not be as good this year,” said Rick Thomason, UT/TSU Johnson County Extension County Director. “This is due to the hot temperatures and dry weather we’ve experienced here in late summer and continuing into the fall. When you have this combination of dry weather and hot temperatures, the leaves just dry up on the trees, turn brown and fall off prior to the pigments being formed in the leaves, which give us the bright fall colors. Many trees have already been shedding their leaves. What color we do have this year is predicted to be a little later than normal. Instead of the peak season for fall foliage in Johnson County is expected in late October, we expect it to be later in November
this year and the mountains not being as colorful this year.”
Prime fall foliage in East Tennessee also varies by elevation as the first hints of fall color begin at the highest points, then week after week, sweep down to the lower elevations and valleys where it tends to be cooler.
Shorter days and cooler — but not freezing — nights help those biochemical processes start changing the leaves’ colors. The University of Tennessee Forest Resources AgResearch and Education Center explains that during summer, it is chlorophyll that gives leaves their green color. This complex chemical, which is essential in the photosynthetic production of food sugars, is continually being manufactured and broken down at approximately equal rates.
Leaf-changing is more than just a scenic occurrence. It is the scientific process that prepares trees and leaves for the winter ahead. As fall approaches, the steadily decreasing length of day and cooler temperatures interact to biologically trigger the formation of a corky layer of cells across the base of the leaf. This formation gradually decreases the supply of water and minerals to the leaf; reduces the manufacture of chlorophyll; and traps sugars in the leaf. When chlorophyll is reduced, pigments become prominent and are responsible for the coloration of autumn leaves.
“Sourwood, dogwood, maple, sassafras and birch trees are the first to make the change, turning red, orange and yellow,” explained Thomason. “At this point, there is just a hint of fall color change among those early autumn starters.”
While temperature, sunlight, elevation, and soil moisture all play a role in how to fall foliage appears, year after year, despite the conditions, the East Tennessee mountains come alive with deep yellows, oranges, reds. This year is no difference, except they may appear slightly later and somewhat muted.