UNIVERSITY PARK, Pa. -- The hottest year on record for central Pennsylvania and one of the driest growing seasons ever are likely to result in a less than spectacular fall foliage display, according to an expert in Penn State's College of Agricultural Sciences.

"I think we have to lower our expectations on what we hope to see this year because the climate has put tremendous stress on some tree species," says Marc Abrams, professor of forest ecology and physiology. "Due to the extremely hot, dry weather this summer, this fall's display will not be one of our best. In fact, some people are probably already starting to see that some leaves are going from green to dull brown."

The hot, dry conditions may also affect the timing of the foliage coloration, Abrams pointed out. "Normally this level of drought would make coloration occur a week or so early," he says. "But it has stayed warm the whole way through September, and that will delay the display. Those opposing forces are likely to mitigate each other to some extent, so we should see our foliage colors peak in the second week of October, as usual."

For about 20 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 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. Much of Pennsylvania experienced a significant drought this summer.

"One thing that I have been impressed with in my 20 years of gauging foliage is the resiliency of the display," Abrams said. "This year I think we may see good color, but perhaps not great color. People should go out and search for those pockets of great color, because they will be there. They just may be a little harder to find this year than usual. If we do get some rainfall in the next couple weeks, that should help brighten the colors."

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EDITORS: Marc Abrams can be contacted at 814-865-4901 or e-mail agl@psu.edu.

Writer/Editor: Jeff MulhollemOffice 814-863-2719