By Lisa Jennings, Natural Resource Specialist at USFS
One of my favorite camp sites when I was younger was in a hemlock grove deep in the Wilson Creek watershed, where I could cool off under the emerald green canopy and the hemlock needles were so thick that I could sleep comfortably on the forest floor. Going back to that site today, it is much different from the magical place of my memories. Now, those towering green hemlocks are dull, grey, and leafless. The forest floor is littered with fallen branches and toppled hemlock trees.
In the last decade there has been a drastic change in the forest communities of the southern Appalachians. Hemlock woolly adelgid, a small aphid-like insect from East-Asia, has decimated hemlocks in eastern North America. First introduced in a private garden near Richmond, Virginia, the adelgid has spread both north and south – from Georgia to New England.
The adelgid attaches to the base of the hemlock needles, where it feeds on the sugars that are being transported from the needles to the tree. Infested trees can be identified by the white woolly mass on the underside of the branch. Over time the adelgid starves out the hemlock, leading to defoliation and eventually death.
Scientists have yet to find resistant hemlocks in the east, leaving active treatment as the only option to save these iconic trees. Maintaining hemlock forests is one of the main goals of the Grandfather Restoration Project, an 8-year collaborative project to restore 40,000 acres of forest on the Grandfather Ranger District as part of the national Collaborative Forest Landscape Restoration Program. Two species of hemlocks grow on the Grandfather District. The more common eastern hemlock grows in streamside forests. The rare Carolina hemlock grows on rocky outcrops. Both species are susceptible to the hemlock woolly adelgid.
The most common way to treat hemlocks for the adelgid is using an insecticide treatment. The Forest Service’s primary chemical of choice is called Imidacloprid. Imidacloprid is mixed with water and injected into the soil around the root system of a hemlock. The chemical moves into the foliage, killing the adelgids as they feed but leaving the foliage unharmed. This both maintains old hemlocks and supports regeneration of new hemlocks near the treated trees.
The other way to treat the adelgid is using a natural predator. Laracobius negrinus, a small beetle from the Pacific Northwest, is a natural predator of the hemlock woolly adelgid. Scientists at the Southern Research Station are studying how these beetles respond to the colder winters in our area, and how we can best use them.
Through the Grandfather Restoration Project, the Forest Service has treated thousands of hemlocks and partnered with leading researchers to release beetles at about a dozen locations on the Grandfather Ranger District. Although we cannot save every hemlocks, we can help preserve the species to ensure this iconic tree remains a component of the forest into the future.
This highlight is part of a series of videos celebrating the mid-point of the Grandfather Restoration Project to provide folks with an inside view into what restoration looks like in the forest. Check out the hemlock preservation video here: https://vimeo.com/159837869.