UNIVERSITY PARK, Pa. -- After watching raging wildfires devour wide swaths of California in October, a forest expert in Penn State's College of Agricultural Sciences points out that Pennsylvania forests have actually become less likely to burn. "Ironically, both our situation here and the one in California have been caused by forest fire suppression," says Marc Abrams, professor of forest ecology and physiology who has earned a number of awards and honors for his 25 years of forest fire research. "Forest fires, often caused by lightning and Native American burning in the past, have been a natural factor in forest ecology across North America for thousands of years, and when we suppress fire, we change the natural order. The eastern forests have become less flammable; out West, they have become infernos waiting to happen."

In California and other western states, where the weather is dryer and forests consist of a higher percentage of more flammable species such as conifers, fire was a frequent occurrence before humans began to suppress the blazes, resulting in the accumulation of litter and deadwood on the forest floor. Now, buildup of that tinder-dry fuel makes fires burn hotter, faster and sometimes explosively. "That, coupled with a decade-long drought, made this fall's fires in Southern California especially devastating," says Abrams. Through his research, Abrams has established that fighting forest fires has contributed greatly to an ongoing change in the dominant tree species in Pennsylvania forests from oak to red maple and other shade-tolerant tree species. Maple was a tree that grew primarily in swampy areas that rarely burned, and oaks -- which have thick bark and deep roots that protect them from fire and the ability to sprout seedlings from the blackened forest floor shortly after a blaze -- grew in the open forests. "When forest fire was suppressed," Abrams explains, "red maples became more common in the open forests away from the swamps. "In my opinion, suppression of forest fire is the major reason for species change in Pennsylvania forests, but it is not the only reason," adds Abrams. "Timbering practices, selective deer, browsing and acid rain are also factors." He points out that loggers took more high-value oaks in the last 100 years or so. Herds of white-tailed deer, which prefer oaks to maples as a food source, grew dramatically. And Pennsylvania soils became more acidic because of acid rain (oaks don't thrive in acidic soils). Another reason Pennsylvania forests are less likely to burn now than they were 200 years ago is the disappearance of white pine, according to Abrams. Historically, this species was abundant in Pennsylvania's forests, which were a much more coniferous environment than today's more hardwood-dominated woods. But the pines were heavily logged by our ancestors, who valued the soft, straight timber for building, and they still have not obtained their former level of dominance. Pitch pines also were common, Abrams notes, and those trees suffered a similar fate. "Litter from hardwood trees is less flammable," says Abrams, "and fires, when they occur in eastern forests, tend to be surface fires rather than tree-crown fires. Western forests are more coniferous in nature, with more flammable foliage. They tend to burn from top to bottom. "Historically in Pennsylvania we had more pines and oaks, both species that are more flammable," Abrams adds. "They have been replaced by maple, birch, cherry and beech, species that don't burn as well."

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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 #293