A Burning Question: Can an Old Tool Reshape Upland Hardwood Forests?
by Carol Whitlock
There is a commonly held view about forests in the South. It goes something like this: Before European settlement, a squirrel could travel from the Chesapeake Bay to the Mississippi River without having to touch the ground even once. What often flows from this view is the less supportable belief that natural processes, not human intervention, were responsible for the dense canopy cover that allowed that squirrel to remain airborne.
In fact, findings from recent studies suggest that humans have used fire to manage southern forests for the last 5,000 years, producing a large and healthy oak presence in the uplands, relatively sparse and parklike understory conditions, and abundant game animals. When Europeans arrived bringing the diseases that killed 90 percent of the native populations, they found thriving villages surrounded by fire-adapted landscapes that supported thousands of acres of agricultural lands—all maintained by regular burning.
In the scramble to rebuild southern forests after the abusive logging, grazing, and mining of the late 19th century, forest owners and managers lost sight of the lessons learned from their native predecessors. The last century has seen a rebirth of a very different forest than the Europeans inherited. The once dominant chestnut trees have been eliminated by blight. In some places, fire suppression has left large quantities of highly flammable material on forest floors. Dense thickets of rhododendron and mountain laurel block seedling growth of species, like oak, that are preferred by many types of wildlife. In mixed oak-shortleaf pine forests, white pine is replacing the shortleaf component and shading out the oak component. And reduction of available nitrogen— released when nitrogen compounds are exposed to heat—has resulted both in a decline of overstory trees and in fewer and less diverse understory plants.
These changes in upland hardwood ecosystems have also opened the way for a host of insects and nonnative invasive plants—and have led to renewed interest in prescribed burning among forestry professionals. Prescribed burning has been used even less in the mountains than in other areas of the South because fire behavior is less predictable and smoke management is more difficult in highly variable topographies. However, the situation has reached a point where the ecological and wildfire-prevention benefits from prescribed burning, combined with advances in burning techniques and smoke management, may cause a shift towards acceptance among upland residents—many more of whom are moving into wildfireprone areas.
Two recent efforts to shift upland forests toward a state that is less stressed and better functioning involve a return to the use of prescribed burning. Both involve research in the mountains of western North Carolina, one at the Coweeta Hydrologic Laboratory near Franklin and the other further east at the Green River Game Land near the South Carolina border. Together they paint a comprehensive picture showing the effectiveness of prescribed burning in reducing wildfire risk and the ecological aftereffects of burning on water quality, availability of nitrogen in soils, competing vegetation, and insects, birds, and small mammals.
Since the 1990s, Coweeta scientists have taken a multiple landscape approach to applying prescribed fire of varying sources, intensities, and severity—monitoring the effects on carbon cycling, water quality, and vegetation. Treatments include standreplacement fire (cutting followed by a prescribed burn that simulates wildfire), low-to-moderate intensity understory burning, and wildfire in old-growth hardwoods.
They found that burning successfully reduces invasive white pines and evergreen shrubs such as mountain laurel with little or no movement of sediments into streams, provided the forest floor is kept intact and vegetation recovery is rapid. Based on these findings, the scientists recommend that fire managers should limit fire severity and size if the goal is to minimize the effects of prescribed burning on water quality, soil nutrient loss, vegetation recovery, and other ecosystem properties.
The restoration work at Coweeta is continuing. In ecosystems that have fallen into decline, scientists are evaluating combinations of treatments such as thinning overstory trees and midstory shrubs followed by prescribed fire and the planting of desirable species.
Green River Study
Ten years after the Coweeta studies began, scientists began new research at the Green River Game Land as a part of the National Fire and Fire Surrogate Study, a network of 13 long-term experiments in different settings across the United States. The purpose of the Green River study was to determine the ecological and economic responses of forests to low-intensity prescribed burning with and without thinning and other mechanical treatments that often serve as surrogates for fire.
The Green River study is ongoing, but Tom Waldrop, the SRS research forester who is leading the effort, says that the early results are encouraging. They show that burning and mechanical treatments reduced litter and other forest fuels, which reduce flammability if a wildfire should occur. In addition, organic material in soils increased after prescribed burning. Although mechanical treatments were more effective at removing mountain laurel and rhododendron than fire, oak seedlings from sprouts and acorns increased after prescribed burning.
Jim Hanula, SRS research entomologist based in Athens, GA, reports that an increase in herbaceous plants in the study resulted in increases in a range of insect pollinators including ground nesting bees, wasps and other flies, and even the rare Diana fritillary butterfly, which has been eradicated from parts of its native habitat in North Carolina.
For the same study, Katie Greenberg, research ecologist with the SRS upland hardwoods unit, monitored the effects of treatments on breeding birds, frogs, salamanders, lizards, snakes, white-footed mice, and shrews. She found that low-intensity fires increased populations of whitefooted mice but had no effect on frogs, salamanders, snakes, and shrews. Among the breeding birds, the only species that decreased in numbers were hooded warblers, which make their nests in shrubs, and worm-eating warblers, which forage and make their nests on the ground and in shrubs.
These studies, while not conclusive, suggest that prescribed burning can have a beneficial effect in upland hardwood forests and the creatures that inhabit them.