The Gypsy Moth Invasion: Can Silviculture Save the Day?
by Zoë Hoyle
There’s an enemy making its way into Kentucky. The gypsy moth, originally imported into Boston in 1869 as part of a failed silkmaking experiment, has moved slowly but steadily south and west towards the Southern Appalachians, sapping the strength of its preferred hosts—red and white oaks—leaving them more susceptible to death from oak decline. Gypsy moth infestations currently cover more than 386,000 square miles, with populations found from Maine to North Carolina and west to Wisconsin.
Gypsy moths are expected to arrive in Kentucky in 2010 or later, moving into oak-dominated forests already weakened by oak decline, a “disease complex” that results when tree age, adverse climate, and site conditions combine with stress from disease or insects to push oaks toward untimely death.
In the Daniel Boone National Forest near Cold Hill, KY, a team of Forest Service (FS) and university researchers and national forest technicians have started an ambitious experiment to find out whether manipulating the structure of forest stands before the gypsy moth arrives can reduce damage from the pest. Set up as a silvicultural assessment under Title IV of the Healthy Forests Restoration Act (HFRA) of 2003, the project will test the ability of four different silvicultural treatments to improve the health of existing hardwood stands and reduce oak mortality.
Callie Schweitzer, research forester with the SRS uplands hardwood unit, coordinates the work among research and national forest personnel setting up the silviculture assessment. This has meant collecting data, selecting stands for the treatments, and keeping the communication going among partners. “Within the next year, the majority of the treatments will be implemented,” says Schweitzer. “Then we’ll start collecting data on how each treatment affects the structure and species composition of the forest, the ability of oaks to regenerate, and wildlife habitat.”
Early into the Fray
Kurt Gottschalk is all for getting the drop on gypsy moth. Research forester with the FS Northern Research Station, Gottschalk has spent over 25 years developing methods to minimize the effects of gypsy moth on oak-dominated forests and to regenerate and rehabilitate them after attacks. He is currently in charge of a Title IV HFRA project on the Monongahela and Wayne National Forests in Ohio, an area where the gypsy moth is already resident or expected within the next couple of years. In an ideal world, Gottschalk would like to see treatments in place 4 to 10 years—or even longer—before infestation.
“Preoutbreak treatments focus on reducing the vulnerability of stands by removing the trees most likely to die and regenerating stands that are close to maturity or understocked,” says Gottschalk. “The most effective control is active forest management before the gypsy moth arrives. Everything you do after infestation is reactionary.” Gottschalk worked extensively with Schweitzer and others on the Daniel Boone project. “We used some of Kurt’s criteria for our initial evaluations of stand health,” says Schweitzer. “He also sent his technical staff to the Daniel Boone to help with data collection, and his forester Dave Feicht helped develop marking guidelines for several of the treatments.”
The situation at the Daniel Boone is complicated by a high level of oak decline, a naturally occurring process that defoliation by gypsy moths speeds up. One round of defoliation will not usually kill a tree, but trees already weakened by age or drought and then stripped of their leaves can be taken down more easily by other organisms such as shoestring root rot or the twolined chestnut borer.
“You can see gypsy moth as a special case, or subset, of oak decline,” says Gottschalk. “In some cases, defoliation by the insect collapses mortality that would occur over 10 years into as little as 2 years.” Data from the Northeast and Mid- Atlantic show that about 20 to 25 percent of the areas defoliated will have 50 percent or greater mortality.
Gottschalk and others have outlined three basic options for dealing with impending gypsy moth infestation: do nothing (the most frequently chosen option); alter the susceptibility of the forest by changing species composition; or alter vulnerability by removing dead and dying trees and improving the vigor of remaining trees by altering stand structure.
The Daniel Boone experiment uses four levels of treatments to both improve vigor and promote oak regeneration. The most intensive treatment, shelterwood harvest with reserves, removes all but the largest trees to eventually create two-aged stands. A second option, oak shelterwood, retains more of the overstory. A third option involves thinning to simply reduce stand density with no special attention given to oak regeneration, while the fourth treatment combines thinning to create a grassy, open woodland habitat with prescribed burning to maintain this condition. Control plots with no treatments, the “do nothing” option, will provide data for comparison.
With over 600 acres of experimental plots mapped out, the silvicultural assessment is one of the largest experiments of its kind and includes multidisciplinary studies on wildlife, stand dynamics using tree-ring data, forest harvesting operations, and the potential of using the wood thinned from plots as biofuel.
“We want to come up with specific recommendations for improving oak regeneration under these situations,” says Schweitzer. “We also want to be able to specify the harvesting operations needed to reduce impacts to soil, and the prescribed burning prescriptions that will sustain open oak woodland conditions on these sites.”
The experimental plots will also be set up as demonstrations areas, where land managers and private landowners can actually see the effects of different silvicultural approaches on oakdominated forests. Jeff Stringer, associate Extension professor at the University of Kentucky, who has already provided funding for data collection and plot preparation, will provide his expertise in technology transfer when the demonstration plots have been installed.
The enemy is still on the way, but the experiments underway will provide new understanding about how managers can help oak-dominated forests weather the storm. “Compared to other invasive insects, gypsy moth is extremely manageable,” says Gottschalk. “If we increase the vigor and regeneration capacity of our forests, they can weather the initial attack with relatively little long-term damage.”
Other cooperators include: The National Wild Turkey Federation, Rocky Mountain Elk Foundation, Kentucky Forest Industries Association, Eastern Kentucky University, and the University of Tennessee.