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.
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.
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!