UNIVERSITY PARK, Pa. -- The mother of all wet summers has transitioned into a soggy fall with the help of a hurricane, but a forest expert in Penn State's College of Agricultural Sciences still expects this autumn's foliage display to be among the brightest.

"Hurricane Isabel could turn out to be a slight negative," says Marc Abrams, professor of forest ecology and physiology. "The 50-mile-per-hour winds that tore through parts of Pennsylvania knocked down some trees and blew away a lot of leaves, but the ones that remain on the trees should be very colorful in a few weeks. This should be a great autumn to look at the foliage."

According to Abrams, the late-summer wetness will not detract much from the brilliance of the display and might even result in brighter colors. "Trees across the state are mostly healthy and, of course, well-hydrated," he said. "The abundant rain was a positive thing for production of leaves, photosynthesis and production of chlorophyll. The unusual amount of moisture did promote certain pathological problems, such as a tree fungus that resulted in some trees losing their leaves early, but that happened in isolated pockets."

Some weather-related things must happen in coming days and nights, Abrams points out, for the foliage display to reach its potential. "First, it needs to stop raining -- a mild fall drought would make the leaves more brilliant," he explains. "And it must cool off. Night temperatures dropping into the 30s and 40s are good for the foliage.

"The worst thing that could happen for the foliage would be if it stayed warm and rainy," he added. "We want to see bright, sunny but cool weather. If we get it, we'll be treated to a superior display."

For nearly two decades, 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 oak.

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EDITORS: Contact Marc Abrams at 814-865-4901 or by e-mail at agl@psu.edu.

Contact:

Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-863-9877 fax #252