UNIVERSITY PARK, Pa. -- If temperatures don't cool down soon, fall foliage watchers in Pennsylvania may see a late peak with less intense colors this year, says an expert in Penn State's College of Agricultural Sciences.
"September's unusually warm weather extended the growing season, so most of the trees are still green and photosynthesizing," says Marc Abrams, professor of forest ecology and physiology. "Also, the dry weather in many areas caused some trees to lose their leaves early, with unspectacular color.
"If the weather doesn't start to cooperate, peak coloration will be a week to ten days late. Colors may peak during the third or fourth week of October, rather than the second week. We also may see less impressive colors, with different trees changing at different times."
For 12 years, Abrams has studied how seasonal precipitation and temperature influence timing and intensity of fall colors in Central Pennsylvania. "We believe that clear, bright days, low -- but not freezing -- temperatures and dry conditions promote the best fall colors," he says.
Cooler temperatures signal deciduous trees to stop producing chlorophyll, the green pigment responsible for photosynthesis, he explains. The chlorophyll breaks down and disappears, unmasking other leaf pigments. It's these other pigments -- called xanthophylls and carotenes -- that create the glowing yellows and oranges seen in the leaves of yellow poplar, hickory, sycamore, honey locust, birch, beech and certain maples.
After chlorophyll production stops, trees also produce another pigment in their leaves called anthocyanin, Abrams explains. The anthocyanins create the brilliant reds and purples seen in maple, sassafras, sumac, black gum and purple oak.
The amount of anthocyanin produced each year is related to starch levels in the tree. Trees often produce less starch during droughts. "Last month, I was concerned about the drought effects in the region," Abrams says. "But we had a good amount of rain in the last week and that may alleviate that problem."
All predictions aside, Abrams says not to worry. "We always have good color in this region in the fall," he says. "The question is: Will we have a good year -- or a great year?"
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EDITORS: For more information, contact Marc Abrams at 814-865-4901.
Contacts: Kim Dionis KDionis@psu.edu 814-863-2703 814-865-1068 fax