Visitors to Great Smoky Mountains National Park are probably already aware of the presence of a tiny killer wreaking havoc on the old growth forest. The killer I’m referring to is an insect known as the Hemlock Woolly Adelgid that is killing eastern hemlocks at an alarming rate.
Known as the “redwood of the east,” eastern hemlocks can grow more than 170 feet tall and can have trunks measuring more than 16 feet in circumference. The tallest hemlock in the Smokies, located in the Cataloochee Valley, is listed at 173 feet in height. Hemlocks are known to live up to 800 years or more. The oldest in the Smokies is more than 500 years old.
The reddish-purple insect, a non-native species originating out of Asia, kills hemlocks by depriving them of nutrients. Hikers and travelers may have noticed a fluffy white “wool” on the needles of the forest giants. As young nymphs, adelgids wraps them selves in a protective “wool” as they attach to the base of the needles in order to suck the sap out of the tree.
The insect was first detected on the eastern seaboard in the 1950s before spreading to the Blue Ridge Mountains and then up through the northern Appalachians to Maine. In Shenandoah National Park alone, up to 90% of all hemlocks have already died due to the infestation.
Infestations in the Smokies were originally discovered in 2002 and have already spread throughout most of the park’s hemlock forest. Will Blozan, an arborist and expert on eastern hemlocks in the Smokies, was quoted in the spring 2008 issue of Smokies Life Magazine as saying that more than 95% of the hemlocks in the park already have adelgids. To give you an idea on the extent of the looming devastation, the Smokies has about 800 acres of old-growth hemlock trees and 90,000 acres of younger hemlocks. In some areas infested trees have already begun to die. It usually takes 4-10 years for the adelgids to kill a tree.
Hemlocks play an important ecological role. They help maintain moisture and moderate temperatures on the forest floor. By providing deep shade, hemlocks keep streams cool which is critical for the survival of trout, crawfish, salamanders and other cold water species. The thick boughs of the hemlock also provide shelter and nesting for birds.
Park biologists and foresters have been using four methods to save the hemlocks: soil drenching (pouring insecticide around a tree base), injection (pumping insecticide into the tree), spraying the canopy and branches, and releasing biocontrol beetles.
To date, the park has released over 350,000 biocontrol beetles to treat 100,000 trees.
The national park recently posted an excellent video on their website offering a close-up view of how adelgids attack hemlocks, the various stages in the decline of the trees, and how biologists are using beetles to control the infestation.
Please click here to see the video.
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