Scientists studied oak regeneration in several mixed-oak forests in Southeastern Ohio, a type of forest that is common throughout Central Appalachia and the mid-Atlantic states. Recent studies at Ohio University and elsewhere had indicated that the number of oak seedlings in these forests was low compared to the number of mature oaks in the forest canopy, also called the overstory. Forest ecologists had theorized that oak regeneration may not be as serious in areas high in light and low in moisture, conditions that are amiable to oak growth.
But a study presented Aug. 14 at the annual meeting of the Ecological Society of America in Albuquerque, N.M., seems to contradict that theory.
"It has been thought that, barring any major disturbance such as fire or biotic influences such as an insect infestation, oak may be experiencing reasonable regeneration on sites of high light and low moisture," said Brian McCarthy, an associate professor in the Department of Environmental and Plant Biology at Ohio University and lead author of the study.
"Interestingly, when we brought the light, moisture and regeneration data together, there was no obvious trend toward improved oak regeneration on well-lit, dry sites," he added. "Some forest managers had hoped that there might be a refuge or a niche where oak could still survive in the forested landscape, but our studies suggest that oak regeneration doesn't look hopeful anywhere."
The cause for alarm, McCarthy said, is that if oak seedlings aren't present in sufficient numbers, the mature oaks in the overstory will be replaced with trees that are faring well in the understory, such as maple or American beech.
"The entire biological web of species that live in these types of forests are adapted to living in an oak forest," McCarthy said. "If there is a major change in the habitat, there could be system-wide effects on all the species of insects, birds and mammals that live there, possibly even to the point that some species of animals or plants could become locally extinct."
This concern is a driving force behind McCarthy's study, which was part of the first phase of a larger project by the Northeastern Forest Experiment Station of the United States Forest Service (USFS) in Delaware, Ohio. About 30 scientists are studying more than 1,000 acres over four sites in Ohio to evaluate the effect of prescribed fire on the regeneration of oaks and other hardwood tree species.
"It's believed that fire differentially kills back thin-barked saplings of species like maple, which is one of oak's competitors in the forests we are studying," McCarthy says. "Repeated fires might provide oak with a window of opportunity in which it has the competitive upper hand. If the oaks can get ahead of the maples in the midstory of these forests, they might stand a chance of getting to the overstory."
For this study, McCarthy, Ohio University graduate student Scott Robinson and forest service collaborators examined the patterns of hardwood regeneration in 108 plots in four stands of a mature mixed-oak forest in Southeastern Ohio. The area studied gets as much as 10 to 15 percent of the available sunlight and has moderately dry soil.
McCarthy collected data for the site condition study in 1995, a year before the sites were burned. His preliminary studies of areas that were burned in 1996 and earlier this year suggest that the burn project is having the desired effect -- more sunlight is reaching the forest floor, which could be good news for oak seedlings.
"Although we're still analyzing the data, I would expect to see a significant increase in light in the understory," he said. "But we will need to maintain this high-light condition for several years before we begin to see any effect on oak regeneration."
The USFS project, which began in 1995, is a long-term effort and is funded by the United States Department of Agriculture.
Contact: Brian McCarthy, 614-593-1615; firstname.lastname@example.org
Written by Kelli Whitlock, 614-593-0383; email@example.com