Forest Stewardship

The Eastern Hemlock Tree: What’s Happening to the Eastern Hemlock?
The Eastern Hemlocks, Tsuga canadesis, are being attacked by the Hemlock Wooly Adelgid, Adelges tsugae, an exotic species accidentally imported from Japan in the 1950’s. The Adelgid is a tiny, aphid-like insect that feeds on the sap of Hemlocks while injecting its toxic salvia into the tree. An Adelgid infestation can kill a 400 year old tree in only 18 months. The once lush, green growth of many Eastern Hemlocks is now brown, brittle, a glaring reminder of the Adelgid’s presence here at Mountain Lake.

Why do we care?
Mountain Lake’s forests are home to some of the largest Eastern Hemlock in the country, including two of the last virgin stands in the Eastern United States. Eastern Hemlocks have both a high ecological and esthetic value. They are an integral species in Mountain Lake’s ecosystems, as they are one of the primary canopy species of the three distinct forest habitats on Mountain Lake property.

The canopy, which is the primary site for energy production through photosynthesis, has a major influence on the rest of the forest. All underlying forest strata; the understory tree layer, shrub layer, herb layer, and organic layer, are directly dependent on the microclimatic conditions of temperature, moisture, and light as well as the physical structure created by the dominant canopy trees. As you might expect, animal species occurrence and diversity are directly related to forest stratification as well.

Why are these ancient trees important?
In Mountain Lake’s forests, as well as many other forests on the East Coast, the Eastern Hemlocks provide a protective canopy. Without this canopy, sunlight will penetrate to the underlying forest strata, and thus cause massive changes in vegetation and consequential wildlife habitat. Eastern Hemlocks are a keystone species here at Mountain Lake and throughout many East Coast forests. They play a significant role in determining the community structure and thus have many plants and animals both directly and indirectly dependent upon them.

“Loss of the Hemlock could be a disaster of mega-proportions, similar to the disaster with the Chestnut blight early in the century, but perhaps even more devastating. When the Chestnuts were killed, several species of oak were able to adequately fill the niche that the Chestnuts previously held. But with the hemlocks, there is no species to do this. This forest could be lost forever.”

Who will be affected?

The largest Rhododendrons in Virginia are found here around Mountain Lake. These beautiful, flowering shrubs grow in abundance due to the environment that the Hemlocks provide. Without the hemlocks; rhododendrons, mountain laurel, ferns, mosses, and countless other species will be affected. Some of the other species include: Leatherwood, Rattlesnake Plantain, Bunchberry, and Goldthread.

Several species of birds are dependent on the Eastern Hemlocks for their survival. They include, the Black-throated Green Warbler, Solitary Vireo, and Northern Goshawk. There are 12 less dependent species. Scientist predict that migratory bird patterns may be disputed by the decimation of the Hemlocks.

Brook Trout
Hemlocks protect streams and lake shores from direct sunlight, keeping the water cold and curbing erosion to help keep the water clear. Aquatic species dependent upon shaded, cool water may not survive without the Hemlocks. Clearly, the loss of the hemlocks could dramatically alter aquatic life in and around Mountain Lake .

What is MLC doing to save the Hemlocks?
The Conservancy is working with scientists from the Department of Entomology at Virginia Tech to research and treat the Eastern Hemlocks on Mountain Lake property. Two primary methods of treatment have been established.

Scientists have been using Imidacloprid, a systemic insecticide, to treat 380 trees along the Indian Trail, Lower Jungle Trail, Blueberry Hill, Pond Drain, and the Girls Camp Road since 2001. Imidacloprid is a broad spectrum insecticide that kills by contact and ingestion by attacking the nervous system of the Adelgid. It has very low vertebrate toxicity and little or no movement in soil.

Scientists have collected invertebrate samples from spring water as well, and have found that no decline in invertebrate populations. Instead, they found an increase in the invertebrate population from 2001 to 2003. Hence, they do not deem the treatment of Hemlocks with Imidacloprid a threat to invertebrate populations. Based on their studies, low levels of imidacloprid did not appear to effect the invertebrate population. The scientists will continue regular sampling of both lake and spring water and invertebrate species, as well.

Scientists have released populations of the Pseudoscymnus tsugae, P.t. Beetle, as a natural, biological control for the Adelgid. The tiny, ladybug like P.t. Beetle was imported from Japan in the early 90’s. It is a predator species from the pest’s native range. It feeds and reproduces on the Adelgid. Studies have shown that releasing thousands of these beetles may be a way to keep the Adelgid in check enough to allow healthy Hemlocks to grow. Populations of the P.t. Beetle have been released on the eastern side of the lake and along Pond Drain Stream. Scientists believe the classical biocontrol of the Adelgid to be cost effective and have little or no non-target environmental impact. Biological control, however, is a slow process, as it takes a long time for the population of a predator species to be established.

What can you do to help?
You can make a tax-deductible donation to the Forest Preservation Fund. This donation will allow the Conservancy and the collaborating scientists from Virginia Tech and the University of Virginia to continue researching and treating the Eastern Hemlock trees. Please join our collective effort to save a population of trees and an ecosystem.
Make your donation!

Research Papers
Impact of imidacloprid on hemlock woolly adelgid (Adelges tsugae) and water quality at Mt. Lake, Virginia
Authors:    Tom McAvoy, Warren T. Mays, Scott M. Salom, and Loke T. Kok
Dept. of Entomology,
Virginia Polytechnic Institute and State University,
Blacksburg , VA 24061

Two groups of hemlock trees were treated with imidacloprid using Kiortz soil injectors and one group of trees with Mauget stem injection capsules from 2001 to 2003. In one group of soil injected trees the density of HWA was reduced by 35%, 14 months after the first and two months after the second application. Tree health declined in all years but not as much as for untreated trees in this group. HWA density was reduced by 52% in a second group of soil injected trees, three months after the first treatment and 93% one year after the second treatment.

Tree health did not decline after there years and was no different than the untreated trees. Stem injected trees showed a 52% reduction in HWA in three months after the first treatment and an 87% reduction one year after the second injection. Tree health of these trees did not change and were no different than the untreated trees. Both groups of trees (soil injected and stem injected) had similar health indices and both treatment methods are providing a similar protection from HWA. Trees that were more than 50 m from a stream or the lake were not treated. However, imidacloprid was detected in lake and spring water in concentrations ranging from less than 0.02 ppb to 1.7 ppb in lake water and 3.5 ppb in spring water. The density of invertebrates in the springs did not change from 2001-2003. However, caution must be used when applying imidacloprid near waterways especially in rocky well-drained soil.


Help fight to save our hemlocks

Eastern Native Tree Society (ENTS):

Twilight of the giants:

Nationally known arborist works to preserve WNC’s hemlocks:

Can One Man Save the Vanishing Hemlock?:

Healing Harvests Forest Foundation

More information coming soon!