Restoring the Forest Before Spongy Moths Invade

Lead SRS forestry technician Ryan Sisk assesses a recently thinned stand of trees on the Daniel Boone National Forest. Photo by Callie Schweitzer.
Lead SRS forestry technician Ryan Sisk assesses a recently thinned stand of trees on the Daniel Boone National Forest. Photo by Callie Schweitzer.

Keeping forests healthy is better than trying to restore them after droughts or insect outbreaks have already killed trees, but identifying future threats is sometimes a challenge. Not so in the Daniel Boone National Forest in the Cumberland Plateau area of Kentucky. Oaks dominate the area, but they are under stress and susceptible to decline, while invasive spongy moths (Lymantria dispar) expand their range every year and will probably reach the Forest within the next several decades. The moth larvae eat the leaves of trees and shrubs, and defoliation could interact with oak decline to kill many trees in the Cumberland Plateau.

“The potential risks led to a proactive partnership among managers, stakeholders, and researchers on the Daniel Boone National Forest,” says U.S. Forest Service Southern Research Station (SRS) scientist Callie Schweitzer. The partnership included four Forest Service Research Work Units (including the Northern and Southern Research Stations), three universities, two natural resource state agencies, private logging contractors, an electrical utility, and many National Forest system personnel from all levels of the organization.

Oak decline is a widespread and long-term forest health issue,” says Schweitzer, research forester with the SRS Upland Hardwood Management and Ecology unit and lead author of an article about the study recently published in the Journal of Forestry. In the Daniel Boone National Forest, as in much of the Cumberland Plateau, oaks are at risk of decline because of multiple interacting factors. The trees are mature, and grow close together, while recent droughts, management histories, and competition between species have already stressed trees. Future stressors include continuing changes in climate and the impending arrival of the spongy moth.

Improving forest health – especially increasing tree and crown vigor – could prevent oak stands from declining while protecting against future spongy moth infestations. The researchers tested various silvicultural treatments, including selective harvesting, thinning, and prescribed burning on stands that were either slightly moist (sub-mesic) or slightly dry (sub-xeric). “We also examined changes in species composition and stand structure, regeneration outcomes, and the cost of the mechanized forest operations used to implement the treatments,” says Schweitzer.

Three years after all the harvesting treatments were complete, researchers found that the remaining younger oaks were growing more vigorously. “This should allow for continued growth of these oak trees into large overstory trees,” says Schweitzer. “These trees should also be generally healthier and have lower chance of mortality during oak decline or spongy moth attacks than under pretreatment conditions.”

The study area is home to several bat species, including Indiana bats, gray bats, Rafinesque’s big-eared bats, Eastern small-footed bats and several others. Protecting these species required not harvesting too many of their roost trees, which often have large cracks in the trunk and peeling bark.

“The characteristics of roost trees for bats are often exactly the opposite of the healthy, vigorous trees we wanted to promote with the silvicultural treatments,” says Schweitzer. “Meeting multiple, sometimes conflicting objectives was challenging.” The complications were also magnified because of the long-term scale of the project.

Although treatments were communicated as part an approved forest management plan, there were some difficulties along the way. “However, partnerships make multidisciplinary research on forest management easier,” says Schweitzer. “The division of objectives and subsequent work follow disciplinary lines, making the research complementary rather than overlapping.”

Read the full text of the article.

For more information, email Callie Schweitzer at

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