By David Jenkins, SC Forestry Commission Forest Health Coordinator:
With the arrival of fall, many of the brilliant colors associated with the season are beginning to appear.
The cooler weather and shorter days are signals for deciduous trees to prepare for the stresses of winter. Trees initiate physiological changes that will help them cope with the much lower winter temperatures. One adaptation is to drop their leaves. Leaves have been producing energy in the form of sugar all spring and summer, but now they are a liability; the freezing temperatures will kill them, and they can be an important source of water loss if they stay on in the winter.
To prepare for abscission, or leaf drop, the trees absorb as many of the nutrients as they can from the leaves. Other pigments that have been masked by chlorophyll’s green are left behind, coloring the leaves yellow and orange. The bright reds seen in red maple, tupelo and Virginia creeper are caused by pigments called anthocyanins. Anthocyanins are interesting because they are produced specifically in response to cooler weather.
The leaves’ colors change predictably in the fall, starting at higher latitudes and moving south. Also, fall colors change first at higher elevations and move down. Fall colors usually peak in mid- to late October in the mountains of North Carolina and about a week later in the Piedmont. The best place to see fall colors near South Carolina is the Great Smokey Mountains, but you will see plenty of color in the Midlands and the Piedmont, one or two weeks later.
The brightness of colors, particularly the reds caused by anthocyanins, is influenced by temperature and humidity before and while leaves are changing hues. Warm days and cool nights produce more brilliant colors, as do bright, sunny days.
Trees that change earliest are the sumacs (brilliant red), hickories (vivid yellows) and sassafras (bright oranges and yellows).