Reacting to Reality: Hemlock Woolly Adelgid Forces Forest Management Decisions

Calming forest scene

Reprinted from Forest Leaves, Vol. 22, No. 3. Edited for length. Original printed in Farming: The Journal of Northeast Agriculture, October 2012

By Patrick White

In an ideal world, timber harvests are premeditated activities, scheduled years in advance as part of a carefully considered forest management plan. Sometimes things outside our control happen. For some woodlot owners, that list includes hemlock woolly adelgid and emerald ash borer. These invasive insects can force decisions to harvest relatively quickly to salvage some value from trees that will soon be lost. While such events present difficult decisions, they provide an opportunity to make choices that will ultimately improve the health of the forest and help protect it against future pests and disease.

David Jackson, forest resources educator with Penn State Extension, recently saw firsthand what woodlot owners in many areas are experiencing when the hemlock woolly adelgid appeared in a 103-acre woodlot managed by Penn State Extension for educational purposes. “You really feel helpless. There are insecticide treatments you can do, but it’s really not practical in a woodlot setting when you’re looking at hundreds and hundreds and hundreds of trees,” says Jackson. (Researchers are working on some biological controls, notably small non-native beetles that eat the adelgid.)

Though no harvest had been planned in the Penn State Extension woodlot, the decision was made to cut 15-acres of infested hemlock to salvage some value. “We were holding off and holding off and finally we decided that if we were going to get anything out of this area we were going to have to make a sale,” he explains. The decision to harvest hemlock, a softwood, must be made in relatively short order to preserve any timber value.

Just as private woodlot owners do, Jackson and his extension colleagues had to weigh the stumpage value against its ecological value in the forest. The reality is that hemlock is a relatively low value tree. If it were a higher value species, the decision on whether to harvest might have been a little different. “With hemlock, the economic incentive to harvest isn’t great. So the decision has to be made about whether the monetary value is worth the disturbance you’re going to see in the forest,” says Jackson. “Often it depends where it’s growing and how easily you can get access to it. Every situation is different.”

At the Penn State Extension woodlot, forest roads were already in place making access easy, and a trusted buyer was available for hemlock pulpwood, so it made sense to harvest hemlock in areas where streams and springs would not be impacted. While the decision to harvest was made relatively quickly, the harvest itself was thoroughly thought out. The main goal was to generate some revenue while still protecting wildlife habitat and water quality. For example, one affected section contained several springs and small drainages that were excluded from the harvest. “We put it in a streamside management zone and decided we just didn’t want equipment in there,” says Jackson, pointing out that this is just the type of scenario facing many woodlot owners. “It helps us show people the importance of leaving undisturbed buffers along streams.”

A harvest forced by hemlock woolly adelgid also presents an opportunity to consider wildlife habitat. “You’ll have an opportunity to leave dead standing trees, called snags, which provide songbirds with insect foraging sites. Over time these trees will develop cavities or holes in them which will provide nesting sites for a wide range of species,” he emphasizes. Dead, down woody debris and standing “snag” trees make great wildlife habitat, Jackson points out. “We marked trees to leave that had holes in them already as well as other dead standing trees to provide nesting or foraging sites for wildlife,” he explains.

Harvesting under any circumstance is also an opportunity to consider regeneration - which species will come in and replace the harvested trees and what species of trees are you leaving. Both will impact the makeup of the next forest. While Jackson says he has heard some reports of a few trees showing resistance and surviving heavy adelgid infestations, seedlings are impacted along with mature trees, so it’s difficult if not impossible to regenerate the forest back to hemlock.

In the Penn State Extension woodlot, the hemlock harvest provided an opportunity to improve the overall health of the woodlot by not only cutting the hemlock but also taking poor quality trees and less desirable species, like black birch, and leaving preferred trees in place. “We left some really beautiful oak behind. In fact, we left twelve different species behind on the harvest site,” says Jackson. “We’re trying to really promote diversity so we don’t end up in a similar situation again by having an area that’s predominantly all one species. You really open yourself up to attack by exotic pests that way.” The opportunity to promote this type of diversity might be as good a reason as any to conduct a hemlock salvage harvest in the face of the adelgid, he concludes.

Finally, woodlot owners with hemlock stands don’t necessarily have to wait until the hemlock woolly adelgid appears to act. It may make some sense to conduct a preemptory harvest. “There have been some studies suggesting that, if you can do it well in advance of the adelgid, thinning hemlock stands can help,” says Jackson. Hemlocks tend to grow in dense, dark groves, which make them perfect for shading and cooling streams. But the crowded growing conditions ultimately hamper tree health. Thinning hemlocks and freeing up the most vigorous individuals can help the remaining trees grow and expand their crowns, making them as healthy as possible to perhaps survive attacks from the adelgids. “It may be something that can help them fight it off,” he explains.

The 103-acre Ag Progress Days Woodlot is located approximately 10 miles southwest of State College. It has been managed by Penn State Extension for nearly forty years under the direction of Dr. Jim Finley. Numerous educational tours and programs are hosted there each year. Dave Jackson can be contacted at 814-355-4897 or drj11@psu.edu.

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