Nature Notes, Past Events

Save Our Hemlocks

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NATURE NOTES: 10 February 2017

By Ken Czarnomski, VP of the Blue Ridge Naturalist Network

At first glance, the magnificent Eastern (Tsuga canadenis) and Carolina hemlocks (Tsuga caroliniana) seem to be losing their ongoing fight to survive the invasive hemlock wooly adelgid (or HWA) Adelges tsugae, which feasts only on them. This aphid, less than 1/32 inch (about the size of a poppy seed), has managed to dramatically increase its rate of infestation in the last decade.

Fortunately, we have several inspirational initiatives supported by grants through federal, state, regional and private contributors that are determined to make a difference, sharing the goals of the Hemlock Restoration Initiative (or HRI), headquartered in Asheville.

The mission of the HWI “is to work with a variety of partners to restore hemlocks to long-term health throughout North Carolina and ensure that both the Eastern and Carolina hemlocks can withstand attacks by the invasive HWA and survive to maturity on public and private lands,” says Margot Wallston, HRI statewide coordinator. New research on the physiology of hemlocks and how they respond to severe conditions such as HWA, drought, air quality and warming temperatures is being conducted. “Still we have not lost all of the hemlocks,” says Wallston. “There are stands throughout Western North Carolina that have not been as heavily hit by HWA as others, for whatever reason.”

The primary method of treatment is systemic. Although effective, chemical treatments are intended as a temporary solution since in the long term, they are costly, need to be repeated and in various locations, are difficult to accomplish. Ben Smith, research scientist of the Forest Restoration Alliance (FRA) in Waynesville and Albert Mayfield, research entomologist and project leader with the Forest Service, Southern Research Station in Asheville, are looking beyond chemical treatment.

One initiative being researched by the FRA includes a hybrid program that would develop a cross between a Carolina and a Chinese hemlock. This effort is intended to support the ornamental, landscape and garden market. “The Carolina hemlock is capable of a cross with the Asian, but the Eastern hemlock is not,” says Smith, who is exploring development of breeding a naturally resistant species. He does this by taking cuttings from found specimen trees resilient to HWA, transplanting them into lab conditions and relocating them to test plots where they eventually can be exposed to field conditions. “It takes about seven years just to turn a generation,” he says.  Yet he remains optimistic because the HWA does not genetically modify as quickly as some other insects.

Mayfield’s research includes growing seedlings into degraded hemlock stands. Developing restoration methods is the Forest Service’s first critical step. This silvicultural strategy is being tried “even before we explore other methods, what we might do with the tools we already have,” Mayfield explains. Dupont State Forest and Cold Mountain hemlocks are being restored and studied using various methods including clearing, opening gaps, fertilization and soil composition.

The Forest Service’s second initiative in combination with universities is a biological one. This is a two-pronged approach introducing two different insects from the Pacific Northwest, a beetle (Laricobious nigrinus) and a predatory cousin of the eastern silver fly.

Each of the programs operates from the belief that the health of the remaining trees can be improved, especially those in the far north where HWA is not as severe. They also share the idea that chemical treatment works and can help stabilize trees, which would give scientists more time to develop their research.

You can also help save the hemlocks by volunteering field time with HRI and through the “Report a Survivor Program” with the FRA.

—Photos courtesy of Margot Wallston