April 19, 2008
Kentucky’s hemlock trees are threatened with extinction by the hemlock woolly adelgid, a beetle originally from Osaka, Japan which has decimated East Coast hemlocks from Massachusetts to Georgia. It has no natural enemies in North America and, with global warming, may ultimately spread as far north as the Canadian Maritimes.
Massive stands of hemlock have died in both the Shenandoah Valley of Virginia — where an estimated 90 percent of hemlocks have been decimated — and the Smoky Mountains of North Carolina, leaving skeletal-appearing standing timber. The aphid-like beetle has been spotted in the Eastern Kentucky counties of Bell, Clay, Harlan, Leslie, Letcher, Pike, Powell and Whitley, as well as in urban areas much farther west in Grayson and Oldham counties.
First introduced in the 1920s to the Pacific Northwest and in the 1950s to Washington, DC and Richmond, VA, the woolly adelgid feeds on hemlock needles, depriving trees of nutrients. Left untreated, the adelgid causes tree death within five to seven years of the initial infestation. The beetle has spread throughout the East Coast from Massachusetts to Georgia, and has been especially devastating to natural stands of hemlock such as those in forests: specifically, the Carolina hemlock (Tsuga caroliniana) and eastern hemlock (Tsuga canadensis).
Alice Mandt, of the Kentucky State Nature Preserves Commission, said that the state is “concerned that Kentucky may lose its hemlocks much like the American chestnut was lost.” To prevent this, Save Kentucky’s Hemlocks has been formed by a consortium of entomologists, foresters, land managers and other public officials and volunteers to identify areas with beetle infestations and to explore additional means of tree treatment.
The hemlocks are a source of food and shelter to several bird species and other wildlife, and their dense foliage also protects streams by filtering sunlight. Lacking the shading qualities of hemlock, oxygen levels in streams decrease as water temperatures increase, affecting fish species and other aquatic life. The blackside dace (Phoxinus cumberlandensis), listed as threatened in the Endangered Species Act of 1987, is federally protected and depends on just such a shaded habitat. Less than three inches long, the dace is found in only eight southeastern Kentucky counties and three Tennessee counties in the upper Cumberland River drainage area. They feed on algae and aquatic insects found in shaded streams. While the dace had been previously threatened by both coal mining and logging activities, the adelgid beetle’s activity poses an additional threat to the dace.
Adelgid infestations are difficult to treat: aerial spray of pesticides — specifically, the chemical imidacloprid — could damage other trees and the residue could enter streams. A fungal growth which can be sprayed on trees is being studied at the University of Vermont, while entomologists at Virginia Tech in Blacksburg, Virginia are studying a Japanese natural predator of the adelgid…but would introduction of yet another non-native species damage forest ecosystems and create further unanticipated problems? Insecticidal soap sprays are effective, but labor intensive and best suited for homeowner application.
Laricobius nigrinus, a beetle species from British Columbia which eats adelgids, has been introduced into some adelgid-infested areas with a degree of success. Both the as-yet-unnamed Japanese beetle and the British Columbian beetle are thought to feed only on adelgids. Very cold winters are also effective in reducing adelgid populations. At this point, the adelgid threat is great enough in Kentucky that officials have only modest hopes of saving a small portion of “heritage” hemlocks in selected parks.
A Science Daily study, which was based on two years of research in western North Carolina, indicates that remaining hemlocks may die within the next 10 years, and that water dynamics of the Southern Appalachian mountains will be affected. According to ecologist Chelcy Ford, of the Forest Service’s Southern Research Station in Otto, NC, “No other native evergreen in the southern Appalachians will likely fill the ecohydrological role of eastern hemlock if widespread mortality occurs…With the loss of this species, we predict changes to stream flow, streamside forest structure, and soil moisture that will have to be addressed by land managers.”
Have you seen the hemlock woolly adelgid in your area? For more information about joining “Save Kentucky’s Hemlocks,” contact either Donna Alexander at the Kentucky Natural Lands Trust (877-367-5658) or Alice Mandt at the Kentucky State Nature Preserves Commission (502-573-2886).
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Photo credits: Gary Braasch, R. Childs / University of Massachusetts and U.S. Forest Service
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