Working with hemlock.jpg

Brian Heath, a forest health specialist with the N.C. Forest Service, demonstrates on Wednesday how hemlock trees are treated to kill hemlock woolly adelgid by pouring pesticides around their base.

The N.C. Forest Service is working to buy time for hemlock trees in Rendezvous Mountain Educational State Forest in Purlear as part of a three-pronged initiative focused on saving these conifers across western North Carolina from a tiny invasive insect.

Since early November, the forest service has treated about 30,000 eastern hemlocks in Rendezvous—from saplings to decades-old trees—with pesticides that kill hemlock woolly adelgids when they feed on hemlock needles.

This chemical treatment is expected to protect hemlocks for five to seven years or possibly longer, said Brian Heath, a forest health specialist with the forest service.

“We’re trying to keep the tree species going long enough to conduct research on genetic resistance and also identify predator beetles” to help insure the long-term survival of eastern and the much less common Carolina hemlocks, said Heath.

He said the treatment will revive a hemlock with as little as 20 percent of the tree still green. He also noted the importance of saving hemlocks old enough (about 20 years old) to bear cones to produce seedlings.

Chemical treatment, predator insects and genetic resistance are the three primary strategies of the Hemlock Restoration Initiative (HRI), created in 2014 by N.C. Agriculture Commissioner Steve Troxler.

Initial funding was through the settlement of a federal air pollution lawsuit against the Tennessee Valley Authority. The HRI received $350,000 of this multi-million-dollar settlement, as well as funds from the U.S. Forest Service, state funding and other public and private sources.

The work in Rendezvous is focused on the Little Fork Creek section at the end of Benny Parsons Road, which is off Parsonsville Road. State prison inmates convicted of non-violent offenses are treating hemlocks there with two pesticides (with active ingredients imidacloprid and dinotefuran) mixed in water and poured around the immediate base of trees.

Each team for the work consists of about 15 inmates and five forest service employees. It’s done under the BRIDGE (building, rehabilitating, instructing, developing, growing and employing) Program, which also is used for wildland firefighting.

Inmates wear protective clothing as they measure the diameter of each tree to determine the volume of pesticide applied. They record diameters and the number of trees treated on paper forms and spray a strip of orange paint on each treated tree.

“We would not be able to afford to do this without” the inmates because it’s so labor intensive, said Heath, noting that under law they must be paid nominal wages. Inmates volunteer for the work, which often is on steep terrain with thick undergrowth.

Also through HRI and BRIDGE, hemlock trees are being treated at Tuttle Educational State Forest in Caldwell County and at South Mountains State Park near Morganton. Similar work with pesticides has been done at other state forests, state parks, state game lands and on private land.

Margot Wallston, with a background in land conservation, plant ecology and outdoor and experiential education, is HRI coordinator.

Wallston is employed by WNC Communities, which Troxler chose to administer HRI. The Asheville-based non-profit is working with public and private partners to secure funding, educate and engage in hands-on work to protect hemlock trees on public and private lands.

HRI’s efforts also include releasing Laricobius nigrinus beetles (Lari beetles), voracious predators that feed exclusively on hemlock woolly adelgids.

Wallston said research is continuing with other insects that appear to hold promise as predators, but they must be carefully vetted to make sure new problems aren’t created with their release. One predator being studied is the Leucopis (silver fly). Like the lari beetle, the silver fly is a native of the Pacific Northwest.

Dr. Richard McDonald of the Sugar Grove community started releasing lari beetles and studying how well they controlled hemlock woolly adelgids in Watauga and other area counties after first obtaining them in the Pacific Northwest. In an interview in 2015, McDonald said lari beetles released in western and northern Wilkes were likely impacting the Asian invaders on hemlock trees in and near the Wilkesboros.

Not all trees are being treated with pesticides in thick stands of hemlock saplings in Rendezvous. In addition to appropriately thinning these stands, this could be beneficial to lari beetles and other predators of woolly adelgids by maintaining their food supplies.

Work is also being done with hemlock trees that appear to be resistant to woolly adelgids, including early stages of a process similar to the development of American chestnut trees that are genetically resistant to a blight that decimated that tree species.

Wallston said environmental factors, such as weather and climate, play a large role in how hemlocks respond to infestations. Other agencies and organizations are conducting the research on these factors and the results are utilized by HRI, she said.

Wallston said hemlocks benefit from sunlight, even though they are among the most shade tolerant of forest trees in western N.C. Sunlight appears to have the opposite impact on woolly adelgids.

Severe cold in the winter of 2015 and a growing population of lari beetles temporarily knocked back woolly adelgids.

Tom McAvoy, senior lab specialist in entomology in the College of Agriculture and Life Sciences at Virginia Tech University in Blackburg, Va., said research shows woolly adelgids suffer about 95 percent mortality when temperatures are between 10 and 15 degrees below zero.

Heath said temperatures 95 degrees or higher also adversely impact hemlock woolly adelgids, which he said appears to be a factor in the comparatively good condition of many hemlock trees in Wilkes.

He said the forest service was pleasantly surprised at the large number and relatively good condition of hemlocks in Little Fork Creek area. “Ten to 15 years ago, we didn’t think we would have many hemlocks left by now.”

Heath added that Virginia Tech researchers working on hemlocks and woolly adelgids come to Wilkes because of the condition of the trees here.

The aphid-like hemlock woolly adelgid was in North Carolina by 1995, and had been confirmed in all counties in the state with native hemlock stands by 2000.

The invasive insects are also on Carolina hemlocks, generally only found on rocky mountain slopes of western North Carolina, east Tennessee southwest Virginia, extreme northeast Georgia and northwest South Carolina.

Hemlocks are considered a keystone species because of the microclimates they create along mountain streams.

Native brook trout thrive in watersheds with hemlock forests and the hemlock canopy serves as habitat and foraging site for many birds, especially neotropical migratory birds.

Hemlocks are browsed by and provide bedding shelter to deer in the winter, they serve as cavity trees to bears and they are associated with more than 100 other vertebrates and countless invertebrates. 

For more details on the Hemlock Restoration Initiative, including how to make donations or volunteer, go to http://savehemlocksnc.org.

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