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Press release from Western Carolina University, shared Aug. 13.
CULLOWHEE – Abundant rainfall during one of the wettest summers in Western North Carolina history may portend a dampening of the intensity of the fall color show this year unless autumn brings vastly drier conditions, predicts Kathy Mathews, Western Carolina University’s fall foliage forecaster.
“With record rainfall during July, the trees in the mountains look healthy and green at the moment, and that’s a good thing for the trees,” Mathews said. “But leaf-lookers need to keep their fingers crossed for some drier weather in the next couple of months in order for us to see the development of vibrant fall leaf color.”
An associate professor of biology at WCU who specializes in plant systematics, Mathews bases her annual prediction in part on weather conditions, including rainfall, during the spring and summer growing season. She believes that the formation of higher levels of pigments in the leaves correlates with dry weather throughout the year, especially in September. The drier the climate, the more brilliant the fall leaves tend to be, with bright red colors especially dependent upon dry conditions, she said.
“There always will be plenty of color in the yellow and orange hues,” Mathews said. “However, if the days remain cloudy throughout September, there won’t be as much of a pop of bright reds on the leaves.”
Yellow and orange hues result from pigments that the leaves make year-round, hiding under the green color of chlorophyll, she said. As days get shorter and nights get colder, the chlorophyll will break down to reveal the pigments underneath.
On the other hand, the red pigments – anthocyanins – are manufactured by leaves mainly in the fall in response to cooling temperatures and excess sugar production caused by lots of sun, Mathews said. “Dryness also causes production of more red pigment,” she said. “Studies have shown that trees stressed out by dry soils and nutrient deficiency produce more red pigment in the fall. Ample sunshine and dry weather is the combination necessary for brilliant fall foliage.”
Another factor in the annual fall color show is temperature. “Cool nights in September, with temperatures dropping into the low 40s, release the yellow, orange and red colors because chlorophyll degrades faster at lower temperatures,” Mathews said. “Temperature may work in our favor this year, as we have seen relatively cool summer months. If this trend continues, colors may be more vivid despite the rainfall.”
In any event, visitors to the WNC mountains this fall should expect good yellow coloration in the tulip poplars, birches, beeches, and hickories, and oranges in the buckeyes, maples and oaks, she said.
And there is an upside to all the rainfall, even if it means less-vibrant fall colors – the leaves should hang around longer, “With healthy, well-watered trees, we should not see much early leaf drop,” Mathews said.
Depending upon the timing of the first frost, the peak of fall color should arrive during the second week of October in the higher elevations, and during the third week of October in the mid-elevations, Mathews said. Because freezing temperatures quickly degrade chlorophyll, leaves peak in color intensity about five days after a frost, she said.
The color change should begin at the higher mountain elevations in late September and continue through mid-November in the lower levels of WNC.
Regardless of when the peak is and how intense the hues are, visitors always can find good fall color somewhere in the WNC mountains, with more than 100 tree species in the Southern Appalachians. That means not only many different colors of leaves in the fall, but also a lengthy fall color season, Mathews said.