by Julie Dodd
Eastern hemlocks, which make up 20 to 30 percent of the trees in Great Smoky Mountains National Park (GSMNP), are under attack by a non-native insect — the hemlock woolly adelgid.
Hemlocks can grow to be 150 feet tall and six feet in diameter and live for up to 500 years. Yet tiny aphid-like insects, the hemlock woolly adelgid, which are just 1.5mm in size, can kill a hemlock in less than five years.
Hemlock woolly adelgid (HWA) were discovered in Virginia in 1951 after being accidentally introduced from Japan.
First detected in the park in 2002, the hemlock woolly adelgid thrived because of the lack of native predators, parasites or climate factors sufficient to provide population control.
To fight the hemlock woolly adelgid, the park developed a nationally recognized program that has protected hundreds of thousands of hemlocks throughout the park.
For more than 20 years, Friends of the Smokies has provided funding to assist the park’s efforts.
“Friends of the Smokies has provided essential support for hemlock conservation, ensuring the program’s continuity,” said Jesse Webster, GSMNP forester. “Without this assistance, hemlocks would face the very serious threat of ecological extinction throughout the park.”
Hemlock woolly adelgid’s attack
The hemlock woolly adelgid attaches to the underside of hemlock branches at the base of the needles. To protect itself, the insect covers itself with a white, wax-like “wool.” The woolly mass can be about one-quarter the size of a cotton swab. The insect then inserts a feeding tube or “stylet” into the base of the hemlock needle.
“They siphon off carbohydrates from the tree, depriving it of essential nutrients and damaging the needles in the process,” Webster explained.
Signs of an infestation include change of needle color from green to gray, loss of needles, and dead branches.
According to the park service, the hemlock woolly adelgid has infested hemlocks on the Blue Ridge Parkway for more than 20 years and in Shenandoah National Park since the late 1980s. In these areas as many as 80 percent of the hemlocks have died due to infestation.
Importance of hemlocks
Saving the hemlocks in GSMNP has been a priority because of the critical role the hemlocks play in the park’s ecosystem.
Their year-round foliage helps prevent extreme fluctuations in stream temperature, stream flow and soil moisture.
Many plant and animal species – including brook trout, migratory songbirds and the iconic salamanders – rely on cool shaded hemlock forest areas for food and habitat.
Hemlocks in the park also help surrounding communities by protecting watersheds from floods and landslides.
Hemlock treatments
The GSMNP Hemlock Conservation Program has evolved over the years and includes both chemical treatments of hemlocks and the use of beetles to eat the hemlock woolly adelgid.
The park’s program has now become a model of hemlock woolly adelgid treatment, used from Georgia to Nova Scotia.
Webster explained that chemical treatments reduce the hemlock woolly adelgid population on individual trees and within stands of trees.
Beetles (Laricobius nigrinus) provide a longer-term biological control, as they eat the hemlock woolly adelgid and reduce their population.
“These beneficial beetles are established in multiple locations throughout the park and are spreading across the landscape,” Webster said.
The use of these beetles is possible due to research and production in the Lindsay Young Beneficial Insects Laboratory (LYBIL) at the University of Tennessee.
“The Lindsay Young Beneficial Insects Laboratory has been a crucial source of beneficial beetle production and has enhanced our understanding of the beetle life cycle,” Webster said.
Locations in the park – insectaries – are also used to raise beetles. Those beetles are transported to LYBIL, which then develops large populations of the beetles.
“These beetles can then be transported to hemlock stands in the park and released into the wild,” Webster said.
Role of seasonal bio-technicians
Seasonal bio-technicians play an important role in the Hemlock Protection Program.
“The bio-techs are the essential ‘boots on the ground’ who perform crucial tasks,” Webster said.
The bio-techs monitor hemlock canopies to assess their health, treat trees for hemlock woolly adelgid, and transport beetles from LYBIL to the forest.
Friends of the Smokies provides the funding for the seasonal bio-techs.
Locations of Eastern hemlocks in the park
Healthy hemlocks that Friends of the Smokies helped protect can be found throughout the park. Webster suggested several trails and locations for seeing hemlocks.
- Cosby Nature Loop, Low Gap Trail, Maddron Bald Trail and Albright Grove in Cosby, Tenn.
- Oconoluftee River Trail in Cherokee, N.C.
- Most of the campgrounds that are accessible by vehicle, such as Deep Creek, Smokemont, Cades Cove and Elkmont,
“The park is dedicated to protecting these foundational trees, ensuring that many old growth hemlock trees, some more than 400 years old, remain on the landscape,” Webster said.
Also, it’s not just the Smokies that benefit.
“Support from Friends of the Smokies has helped save hemlock trees beyond park boundaries, from Georgia to Canada, through collaborative research and efforts.”
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You can make a donation to Friends of the Smokies to support the Hemlock Conservation Program.