Mighty oaks from tiny acorns grow, though perhaps not as quickly or vigorously as foresters and landowners would like.
Although mature stands of oak and hickory dominate the forested slopes of our Blue Ridge Mountains, foresters have been sounding an alarm about the future of these species, particularly the economically and ecologically valuable oak, since the 1950s. That’s because when those forests are harvested, other types of trees — notably yellow poplar — start crowding them out.
Poplar also has various industrial uses, including plywood, mulch, paper pulp and fuel pellets. Unlike oak, though, yellow poplar isn’t threatened, and the ramifications of the loss of today’s hardwood forests extend well beyond the purely economic.
At the U.S. Forest Service’s Southern Research Station in Asheville, Tara Keyser has spent years working on the vexing problem of oak regeneration. And since 2009, she’s pushed for a long-term study to determine whether an innovative forest management approach can help this species regenerate.
Keyser recently led a group representing the Appalachian Woodlands Alliance to the 150-acre tract in Bent Creek where foresters will test her approach over the next several decades. The alliance, a loose coalition of public and private entities, seeks to foster sustainable forest practices across the Blue Ridge region.
“I’ll be retired by then,” Keyser said with a laugh. “I tell people, if I studied corn, I’d have results every year. But with trees, these things take longer.”
Bourbon barrels and bear mast
The most prominent oak varieties in the Southern Appalachians fall into two groups, the red (including Northern red, black and scarlet oaks) and the white (white and chestnut oaks), Keyser explained.
These species offer both humans and animals an astonishing list of benefits. Oak is in high demand for furniture, flooring, firewood and even barrels for aging whiskey and other spirits. Acorns are a critical food source for wildlife, from deer and turkeys to squirrels and mice.
Concerns about the future of this critical species have inspired “scores of research papers” as well as “a rather extensive body of research-based guidance for regenerating and managing oak stands,” according to a 2011 paper in the journal Forest Ecology and Management titled “Change in Oak Abundance in the Eastern United States from 1980 to 2008.” Despite widespread anxiety, however, science has yet to deliver either a conclusive explanation of the phenomena responsible for the decline or reliable ways to reverse it.
The Southern Appalachians’ current forest landscape, said Keyser, reflects a history of land-use disturbances tracing back to the region’s native inhabitants. Starting about 12,000 years ago, when boreal tundra gave way to mixed hardwood forests, the Cherokee used periodic fires to clear land for agricultural use and thin the forest understory, creating habitat for wildlife and making it easier to harvest chestnuts.
When European settlers arrived, they adopted many of those management practices, including both controlled burning and tree girdling. These techniques, along with grazing livestock and settlers’ prodigious use of wood for heating and cooking, created a more open forest canopy, with greater amounts of light reaching the forest floor than is typical today.
At the beginning of the 20th century, however, widespread clear-cutting leveled many of the region’s forests, triggering severe erosion and serious environmental degradation. And after the forest resources had been extracted, said Keyser, the local economy began to transition away from agriculture. People moved to cities, and large areas of land were essentially abandoned. “So we went from frequent, low-intensity, sometimes moderate-intensity, disturbance every few years to a period when we just kind of stopped disturbing the forest altogether,” she explained.
Meanwhile, a national policy of fire suppression also took root, and the American chestnut blight wiped out a species that had constituted up to half the forest canopy. As those towering trees died out, however, oak species slowly took their place, “And thank goodness they did,” said Keyser, since the acorns provided an alternate food source for wildlife.
In fact, added Forest Service research ecologist Katie Greenberg, acorns are “one of the main bases of the food chain: If there’s a lot of mice and squirrels and chipmunks, there’s going to be a lot more hawks and other predators.”
But in the wake of the timber harvests of the 1960s, ’70s and ’80s, the Forest Service began seeing yellow poplar as a “very aggressive species” that was outcompeting oak and hickory seedlings, noted staffer Jason Rodrigue.
No silver bullet
There are three ways that forests can regenerate after a disturbance, Keyser explained: from seeds blown in on the wind, sprouts from stumps, or seedlings that were already present.
Oaks and hickories, though, almost always regenerate from either stump sprouts or existing seedlings. But to put up a good fight in the competitive forest environment, research has shown, oak stumps must be from trees less than 8 inches in diameter — and in today’s mature forests, such specimens are few and far between. Oak seedlings, meanwhile, must already be quite large when the forest disturbance takes place.
“When I say large,” Keyser clarified, “I mean over your head. How many folks, walking through the forests around here, encounter oak seedlings over your head?
“Yeah, it doesn’t happen,” she went on, explaining that in the low-light conditions at the forest floor, oak seedlings may be numerous, but they only grow to about 1 foot tall.
Yellow poplar, however, can outcompete other trees in all three regeneration pathways. Even where there are abundant small oak seedlings, yellow poplar seeds can ride in on the wind and overtake the oaks before they can establish dominance in the canopy. “Poplar wins every time,” Keyser said sadly.
Before the extensive logging in the early 1900s, Keyser hypothesizes, oak seedlings reached a competitive size under the era’s more open forest canopies. Those hardy trees, large enough to hold their own against other species, grew into today’s hardwood forests.
But when mature forests are logged now, said Keyser, “Our oaks are in a noncompetitive position. We tend to get a stand that has a large yellow poplar component.” The problem isn’t limited to the Blue Ridge, she noted: “It extends all the way from Missouri and Arkansas to us here, and even up into the Allegheny region.” And despite decades of research, “We still haven’t found a silver bullet in terms of regenerating oak — which tells you just how difficult it is.”
Mind the gap
Keyser based her Bent Creek study on a German forestry technique developed to encourage greater species diversity. The “femelschlag” approach emulates natural or historical forest dynamics, using small- to medium-scale gaps in the canopy to promote the regeneration of less competitive tree species.
Within the next two years, foresters will cut quarter-acre and 1-acre gaps totaling 25 percent of the overall study area, removing all the trees. Ten years later, a second round of cuts will extend the perimeter of those gaps, harvesting the mature trees while leaving the seedlings. Successive harvests will continue the process till, eventually, the entire study area has been affected.
And while Keyser fully expects light-loving yellow poplar to dominate the central portions of the cleared areas, she hopes to see more shade-tolerant species such as oaks and hickories competing successfully in the mixed-shade environment along the edges.
“Out in the periphery, what you get is an alteration of the light environment. You have oak that, over the course of five years, will go from 1 foot tall to something that’s over your head,” she explained. And as subsequent harvests give those larger seedlings more light and room, it may encourage them to take their place in the forest canopy alongside the yellow poplars.
Other species also stand to benefit, added Keyser: “I don’t want to say that the magnolias, the dogwoods, the ashes and the cucumbers [a variety of magnolia] aren’t important. They generally respond to the same light environment that oaks do, so hopefully we’re going to conserve the diversity that’s out there by generating those as well.”
A private matter
The approach, she said, has been designed to be replicable by private landowners. That’s a key consideration for restoring oak populations in the South, where, according to the Southern Forest Futures Project, 86 percent of the forests are privately owned.
Over time, the multiple harvests envisioned by Keyser’s approach could yield an income stream while leaving most of the forest canopy intact. If the study succeeds in encouraging oaks and other species to regenerate, it will give landowners a way to improve the health and economic value of their forests while still providing wildlife habitat, protecting water quality and preserving recreational opportunities and views.
But the gap technique won’t be a good fit for every site and situation, she emphasized. Multiple harvests require a good road infrastructure, which probably won’t be economically feasible in very steep and/or remote areas.
And like the slow-growing oak itself, Keyser’s study will take a long time to bear fruit. The 40-year waiting period is daunting, she admits, but foresters have few alternatives. “Our oak silviculture toolbox is pretty limited, so we hope it’s going to be a useful tool,” she concludes.