Hemlock Woolly Adelgid infestation/threat to the Smoky Mountains National Park

GSMNP Seasonal Road Closures: Active

Hemlock trees dominate the Great Smoky Mountain Park as they are the most common tree found within the national park and often the largest in any given area. Hemlocks present their green color year round from the valleys to the mountain tops of the park and are crucial to the ecosystem of the entire Smokies.

The hemlock tress not only offer a habitat for the local birds and other animals that reside in the national park, but also supply much needed shade to creeks and streams keeping them cool during the summer which benefits the fish and aquatic plants and animals that reside in the waterways of the Great Smoky Mountain National Park.


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The hemlocks cooling effect on the creeks, streams and waterways of the Smoky Mountains can be can make much as a 7 degrees (Fahrenheit) which can make a huge difference to some of the more fragile species and has helped the native Brook Trout restoration efforts possible in some of the bodies of water that receive more sunlight.

From shaded valleys to sunny mountains and hillsides, the Eastern hemlock tree (Tsuga Canadensis) these hearty evergreens can be found in elevations up to 5,000 feet or more. Hemlocks have great shade tolerance and can live more than 600 years - far longer than most of the surrounding hardwoods and evergreens found throughout the Smokies. Since they live so long and are such a dominate species they can easily grow to heights greater than 150 feet.

The Great Smokies Mountains National Park is home to the tallest Hemlock tree which is more than 165 feet tall and 17 feet in circumference can be found in the Greenbrier section of the park. The National Park is also home to the largest stands of old growth eastern hemlock found in the Eastern United States.

The hemlock tree features short needles that are from 1/3rd to 2/3rd's of an inch long. The hemlock needles are flat, flexible, blunt tipped and soft and when you look on the underside of the needles you will be able to see 2 pale lines. The hemlock needles are not grouped in bundles which is typical of most of the other evergreen pine tress found in the Smoky Mountains. Hemlocks also have abundant small pine cones that can be found attached to the underside of the stems. The bark of a hemlock tree is brown, deeply furrowed and thick.

Since Hemlocks are such tall trees and they have flat densely packed needles on branches with a wide circumference they make an excellent shelter for birds and small animals of all types. A wide variety of migratory birds such as the Wood Thrush, Warblers: Blackburnian and Black-throated Green, and the Blue-headed Vireo especially love the shelter of the hemlocks.

Now that you see how important to the entire ecosystem the eastern hemlock are to the Great Smoky Mountains National Park, you can understand why any threat that might eliminate this valuable resident of the Smokies is detrimental.

Meet the hemlock woolly adelgid which is such a threat. This tiny unwelcome insect made its way to the eastern US form Asia in the early 1950s. Though small in size, this insect is capable of destroying both young and old hemlock trees by feeding at the base of the hemlocks needles.

Once the hemlock woolly adelgid starts feeding on its host, the end is sure to come. The woolly adelgids feeding disrupts the nutrient flow from the needles to the rest of the tree and eventually will cause the death in anywhere from 3 to 10 years to the host hemlock.

To date there has been no discovery of any natural resistance that the trees may have. Hemlocks trees will also not resprout and grow back from roots unlike some other trees in the park.

Scientists now feel that the hemlock woolly adelgid pose the greatest ecological threat to the park Ecosystem and without intervention most or all of the hemlock trees found throughout the Smoky Mountain National Park will die.

This kind of devastation of the hemlock has already been seen in places such as the Shenandoah National Park in Virginia where at least 3/4 of the hemlocks are infested. Damage to forests from woolly adelgid can be observed from South Carolina up north to southeastern Canada.


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There is some hope for the hemlocks in the Smoky Mountains - make that SOME hemlocks.

Right now there are 3 methods are working to reduce or eliminate the hemlock woolly adelgid form limited treated areas. These methods are:

Systemic treatment of the soil around hemlocks: Treating the soil with insecticides that are absorbed by the roots of the hemlock trees which disperse the insecticide throughout the tree - expensive yet effective for treating single specimens or small groups of trees. This method of adelgid is completely impractical for treating the millions of hemlock trees throughout the national park.

Spraying Insecticidal soap on infested trees: This highly effective method insect control requires saturation of the entire infected trees branches and needles at least twice a year. Spraying can be accomplished by truck mounted units or for further in off the road backpack units and unfortunately aerial spraying does not work. Spraying is effective for the trees that can be reached and does virtually no harm to the environment but is very labor intensive.

Biological control of adelgid by release of predatory insects: In this case a tiny predator beetle called Pseudoscymnus tsugae which was native to Japan where the woolly adelgid originated is released to the environment. This tiny insect is capable of spreading over infected areas hunting down the adelgids. This beetle's only food source is the woolly adelgid which is why the park service is able to import this exotic species into the park without worrying that it may damage the ecological balance of the park.

Testing of this biological control has been conducted since 1992 and both Government agencies and private organizations have been experimentally releasing this beneficial insect since the late 1990s with great success. In test areas the predatory beetle was able to reduce adelgids populations from infected areas from 47% - 87%.

Since 2002 the National Park Service began releasing predator beetles in the Smoky Mountains National Park. Starting slowly the park service released approximately 50,000 beetles in 2002 and 2003. The cost of purchasing these beetles from suppliers is approximately $1 per beetle.

Now for the kicker, the Park service officials estimate that at least several million of these expensive beetles need to be released in order to bring the adelgid under control. Besides the tremendous costs involved, all the beetle suppliers combined can only supply a little less than a million beetles a year - far less than what's needed right now.

The park service needs your help. Not tomorrow - today.

Become a member and make a donation to the Friends of the Smokies who will help by purchasing more spraying equipment, insecticidal soap, predator beetles and other supplies.

You can volunteer to work on programs to help save the hemlocks in the Smokies by contacting (865)436-1200.

You can also learn more about the hemlock woolly adelgid by visiting the following web sites: www.nps.gov/grsm or www.saveourhemlocks.org.


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