What Does Restoration Look Like? Saving Hemlocks

Hemlock Preservation from Lisa Jennings on Vimeo. 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. 

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.

Signs mark treated Carolina hemlock trees

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.

Saving a Keystone Species: Hemlock Restoration on the Grandfather RD

Introduction of the invasive Hemlock Woolly Adelgid (HWA) to the Eastern US has wreaked havoc on the native hemlock species, leading to range-wide declines and total loss of hemlocks in many areas in the Southern Appalachians. In late October, the Grandfather Restoration Project collaborative group got together for a fieldtrip to explore potential for expanded work on hemlocks. This includes both treatments of Hemlock Woolly Adelgid (HWA), which have been taking place on the district for close to a decade, and hemlock restoration, which is a new concept both for the Grandfather Ranger District, and throughout the range of Eastern and Carolina hemlock.

Collaborative members discuss hemlock restoration along the Kitsuma trail

Joining us on this trip were 3 of the leading experts in hemlock research in the Southern Appalachians.

Chelcy Miniat, Research Project Leader from Coweeta Hydrological Laboratory, presented on the hydrological impacts of hemlock loss. Hemlocks provide an important role in riparian forests, regulating stream flow and shading streams from winter sun. As hemlocks die, they are generally replaced by rhododendron, and to a lesser extent water-loving hardwood species. This replacement has been found to lead to higher stream flows in the winter, and lower flows in the summer. Chelcy and her team also tested the effectiveness of the manufacturer recommended treatment dosages for imidacloprid, the main pesticide used to treat HWA on helmocks. Her research determined that the recommendations under-treated large trees, a finding that our silviculturalists can use in their management of HWA.

Bud Mayfield, Research Entomologist at the Southern Research Station in Asheville, spoke about current research on predator beetles that feed on HWA. These predator beetles provided a non-chemical treatment option, and are an important part of an integrated pest management approach to HWA treatments. The predator beetles Bud studies, a species called Laricobius nigrinus, are native to the Pacific Northwest. Compared to other potential predator beetles, they have a higher tolerance for cold Southern Appalachian winters. While predator beetles alone cannot keep up with the adelgid infestations alone, Bud’s research found that combining chemical HWA treatments with predator beetles allowed treatments to be effective longer, reducing the amount of pesticides used.

Robert Jetton, Research Professor at NC State University and Hemlock Project Leader at CAMCORE presented on species conservation efforts. CAMCORE, a non-profit tree conservation organization, has been collecting seeds from Carolina and Eastern hemlock populations in the Southern Appalachians for over a decade. With seeds in cold storage from hemlock populations across the Grandfather Ranger District, CAMCORE provides a seed bank repository for the Forest Service to be used in replanting the species. In addition to seed conservation, Robert is starting work with the US Fisheries and Wildlife Service to map all existing Carolina hemlock populations in order to more fully understand the distribution of the species and its conservation needs.

Treated Carolina Hemlocks along the Kitsuma trail

The collaborative also discussed current and future hemlock work on the Grandfather. Currently, we are treating Eastern hemlock trees that remain alive on the district, and are working to expand Carolina hemlock treatments with the help of CFLR funding. When treating mature hemlocks, young trees within a 10 meter radius of the treated mature tree also benefit from the effects of the pesticide treatment. However, beyond the ambient effect of treatments on regrowth nearby, there is little chance for young hemlocks to reach the over story, as HWA infests both young and old trees. Thus, planting of hemlocks was discussed as an option to supplement this new generation of hemlocks.

Eastern Hemlocks are considered a keystone species in stream-side areas, where they provide habitat for a variety of wildlife species. Unfortunately, there are no substitute evergreen tree species that grow in the streamside zones that Eastern hemlock occupies in the Southern Appalachians. So, even though there are no existing resistant varieties of Eastern hemlock, planting native Eastern hemlocks back into areas that we are currently treating, and committing to a long-term treatment plan for those hemlocks, is a viable option to ensure the persistence of the species and its role in the ecosystem. The members of the Grandfather Restoration Project are just starting to look at options for hemlock restoration plantings, and will be forming a sub-committee to discuss desired conditions and methods for restoration with minimal vegetation disturbance. We are excited to be working with the research community to take the first steps toward restoring this important keystone species on the Grandfather Ranger District!