The Redwood of the East
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, they are a “keystone species.” A keystone species is one that plays a critical role in its ecological community, a role 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 US, enabling it to freely feed on and kill hemlocks in as few as three years. Do I have hemlock woolly adelgid on my hemlock trees? See photos of hemlocks and the adelgid insects.
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 2011 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.
Here is a map showing the spread of hemlock woolly adelgid in Tennessee.
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. Learn more about treating hemlocks on private property.
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. Therefore, 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 US. 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. For that reason, they are only a partial solution at best.
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 charged with protecting threatened hemlocks.
On private property, we look to you.
What The Nature Conservancy Is Doing Across 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 against HWA there. 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. Our work includes administering treatments, coordinating professional training and education on HWA treatment, and leading the development of a map and strategic plan for hemlock conservation areas on public lands on the Cumberland Plateau and Mountains based on high-definition satellite imagery. The map and a plan to systematically target hemlocks for treatment across the state will be complete in early 2012.
How You Can Help
FAQs and Resources
Other Forest Pests
Hemlock woolly adelgid is not the only forest pest threatening our forests in Tennessee. Visit this excellent site maintained by the Tennessee Division of Forestry.