Red maple trees are becoming increasingly dominant in forests throughout the eastern United States, and that worries Kim Steiner. A professor of forest biology at Penn State University, Steiner said that “not only is red maple less valuable as a timber tree, but it doesn’t offer anywhere near the ecological advantages of oaks. Acorns are important food for squirrels and deer and mice and turkeys, so oak is the breadbasket of the woods.”
Steiner has investigated natural regeneration processes and silviculture practices in central Pennsylvania to try to model what has been taking place in historically oak-dominated forests. He and his colleagues examined the development of seedlings and stump sprouts from red maple and oak following timber harvests on state forest lands, and they found that red maples have a remarkable ability to quickly capture growing space at the expense of oaks.
In their study plots, where mature oaks were three or four times more prevalent than red maples in the canopy before harvest, red maple seedlings were nevertheless far more abundant both before and after harvest than oak. And while maple seedlings don’t grow as fast as oak seedlings on average, the tallest red maple seedlings were still as tall as the tallest of the oaks early on. “Through age seven, red maple is pretty much equal to or even a little superior to oak, from seed regeneration alone after having been a subordinate species in the prior stand,” Steiner said.
The tipping point for the changing dominance in the forest, he said, came when they examined red maple regeneration from stump sprouts. He noted that in oak-dominated forests, there are often far more red maple tree stems than oaks – those stems are just much smaller than the oaks – so, because smaller diameter stumps tend to sprout more vigorously than larger stumps, there is greater potential for sprouts from maple. Steiner found that, of those that were cut, more red maples sprouted than oaks, and the maples had a higher survival rate over time and grew a little faster, too. Seven years after harvest, the growing space occupied by red maple stump sprouts exceeded that of oak sprouts by a ratio of 3.5 to 1. An examination of older forest stands found that this red maple dominance after harvest continues for more than 20 years.
Several factors have set the stage for this regime change: fire suppression, which leads to an increase in red maple as light levels decline in the understory; invasions of gypsy moth and other exotics that have negative effects on oaks; and the increasing abundance of deer, which prefer to browse on oaks over red maple. But the biggest factor, according to Steiner, is logging.
“If we didn’t do anything to the woods, the increasing dominance of red maple would be a very slow process,” he said. “But the balance tips dramatically when we cut the stands. When we harvest a mixed oak stand that has all these small red maple trees in it, perhaps what we should do is kill those red maples with herbicide before doing the harvest. Our study indicates that silvicultural practices need to be modified if oak is to be favored.”