The branch of a hemlock tree hangs over brown leaves.
Hemlock Branch Hemlock woolly adelgid threatens Tenneessee's hemlocks. © The Nature Conservan

Stories in Tennessee

Hemlocks and How to Save Them

Our majestic hemlock trees are under attack. Learn what you can do to help save them.

man applying hemlock chemical treatment
Hemlock treatment A National Park Service ranger gives a hemlock a protective chemical treatment using the soil-drench method. © National Park Service

At Fiery Gizzard trail in Tennessee’s South Cumberland State Park, there are towering hemlock trees that are well over 200 years old. In fact, one huge specimen near the northern trailhead is estimated to be more than 500 years old.

Sometimes called the “redwood of the east,” eastern hemlocks (Tsuga Canadensis) are slow-growing, long-lived evergreens that can grow to more than 150 feet tall. Eastern hemlocks and their close relative Carolina hemlocks (Tsuga caroliniana) provide dense shade that keeps forests and streams cool throughout much of eastern Tennessee, especially in the Smokies and on the Cumberland Plateau.

For this reason, hemlocks are a “keystone species"--one that plays a critical role in its ecological community that is much larger than its abundance would indicate. Many forest and aquatic species depend on the presence of hemlocks.

Hemlocks Under Attack

Hemlocks in Tennessee are under attack by an invasive insect known as the hemlock woolly adelgid (HWA). Native to Asia but now living in the eastern U.S., hemlock woolly adelgid have no natural predators in the United States, enabling it to freely feed on and kill hemlocks in as few as three years.

Adelgids were first spotted in east Tennessee in 2002 and have killed many hemlocks in the Great Smoky Mountains National Park and the Cherokee National Forest. In both places, hemlocks are being treated to combat the invasion. Each year, new infestations have been found in the native range of hemlocks and are being documented on a county basis by the Tennessee Division of Forestry (TDF).

As of early 2013, most counties with native hemlocks have noted presence of hemlock woolly adelgid, and in the next few years all counties will likely have adelgids present. It is believed that HWA is spread mainly by birds.

A brown and white map of Tennessee counties.
Hemlock Infestation A map of hemlock woolly adelgid infestation in Tennessee. © TN.GOV

What Is the Cure?

Chemical treatments are available to aid in stopping the adelgids from harming the hemlocks. Treatments periods can range from a year up to five years or more. 

Chemical treatment, though, is not the ultimate answer statewide. While an individual landowner may be able to afford to treat hemlocks on his or her property, on a statewide scale the cost would be too high for state funding. 

The goal is to find the right mix of biological and chemical controls. Predator beetles are an example of a biological control, and have been imported from Asia and the western U.S. After careful quarantine and studies, beetles have been released, and there are signs that they are assisting in the control of the adelgid. Predator beetles are costly, however, and the process of learning how best to use these beetles is just beginning. For that reason, they are only a partial solution at best.

A hemlock tree trunk emerges from a forest floor.
Hemlock Tree Trunk A hemlock trunk is fully rooted in a layer of talus. © Creative Commons/Nicholas A. Tonelli

Who Is Responsible for the Cure?

On public lands, the Tennessee Division of Forestry, the Tennessee Wildlife Resources Agency, the Tennessee Department of Environmental and Conservation, the National Park Service and the U.S. Fish and Wildlife Service are responsible for protecting threatened hemlocks. On private property, the Tennessee Division of Forestry can help landowners. 

Action in the Cumberland Plateau and Mountains

Hemlock woolly adelgid has not yet fully infested the Cumberland Plateau and Mountains, so there is a window of opportunity to plan a coordinated defense. The Conservancy has been actively working with state and federal agencies and other partners to combat the infestation of invasive hemlock woolly adelgid insects in our hemlocks.

TNC's work includes developing maps from satellite imagery to locate and map hemlocks on public lands, administering treatments, and coordinating professional training and education on HWA treatment. We also participate in the Tennessee Hemlock Conservation Partnership (THCP) Executive Committee to plan for hemlock conservation area treatments on the Cumberland Plateau and Mountains. 

On TNC's Tennessee preserves, we have treated hundreds of trees in partnership with the National Park Service, the Tennessee Hemlock Conservation Partnership, private landowners, and the East Tennessee Climbers Coalition. The treatments will protect the hemlocks against woolly adelgid infestation. Our treatments were funded with assistance from Eastman Chemical Company, the National Park Service, and the U.S. Fish and Wildlife Service.