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Protecting The Eastern Hemlocks That Keep Our Water Clean

October 29, 2023

Projected to be the largest stream restoration in Tennessee, the Cumberland River Compact is taking action to provide clean drinking water and thriving habitat while protecting the Eastern Hemlock along the way.

“Ghost” hemlocks alongside healthy Eastern Hemlock trees at Fall Creek Falls in the Cumberland River Basin. Credit: Katie Biggert, Tennessee Department of Forestry.

We’re squeezed three across in a dusty all-terrain vehicle, bouncing through an endless field of chest-high grass, ragweed, and the occasional corn stalk. An American goldfinch careens by, startled from a peaceful day of seeking out late summer seeds. It’s nearly 89 degrees at 10am, but we’re aiming for the stands of trees in the distance where we’ll find shade and the focus of the day – the Eastern Hemlock. Tia King, a scientist and our UTV driver for the day, pulls to a stop as we reach long lines of trees that follow the streams winding through this agricultural land. 

“Meet you back here at 2:30?,” she asks as she helps to unload piles of gear. The goal today is to inoculate Eastern Hemlocks against the wooly adelgid, a parasite that has been decimating the species in the Eastern US for nearly 75 years. Jed Grubbs, In Lieu Fee Program Manager, is leading this large scale stream restoration project at the Cumberland River Compact in partnership with Resource Environmental Solutions, one of the nation’s leading ecological restoration firms.

Covering approximately 137 acres and nearly 10 miles of stream, “Fire Tower”, named for one of the features on the land, is projected to be the largest stream restoration project in Tennessee history.

Located in Van Buren County, TN, just a little south of Cookeville, the streams running through the land are adjacent to treasured state parks such as Fall Creek Falls, Rock Island, and countless named and unnamed waterfalls. These are also the headwaters of the Caney Fork and provide cool waters for sensitive species downstream – including extremely rare species of darters and mussels, and giant aquatic salamanders known as hellbenders. 

The land has been used for primarily agricultural purposes for many decades, the streams have degraded due to cattle waste contamination and grazing too close to delicate native habitats. Once the soil around a streambank starts to erode, the problems escalate. Dirt and silt fall into the water muddying the clear steam and clogging fish gills. Plants that provide food and shelter for birds, turtles, salamanders, have no soil for roots to grip on to, each rainstorm washing more away. Riffles – stony protected spots in the river that provide habitat for crawfish and frog spawn – disappear.

Healthy streambank at the Fire Tower restoration site that has not been impacted by cattle grazing. Photo: Jed Grubbs, Cumberland River Compact’s ILF Program Manager.

It’s conditions like these that threaten the biodiversity of the Cumberland River basin. The 18,000 square miles of the basin host more species than most places on earth. Loss of this habitat, and the species that populate it, is not only a regional tragedy, but a blow to the ongoing work to maintain our planet’s ecosystems. The size of this parcel of land and the unique ecosystems it houses, made it a prime candidate for restoration. While many parts of the Fire Tower site need full stream restoration – regrading streambanks, invasive species removal, restoring native plant populations – the section we are at today has avoided the worst impacts of nearby cattle grazing. 

The threat instead comes from a small, aphid-like insect, the invasive wooly adelgid (Adelges tsugae) that has ravaged populations of Eastern Hemlock. The parasite was introduced to the U.S. in the early 20th century, but it wasn’t until the 1980’s when the wooly adelgid reached the hemlock rich forests of Appalachia that the potential devastation became clear. Hitching on birds, animals, and even people, the wooly adelgid has spread without stop and now infects 21 states from Maine to Alabama (Hemlock Woolly Adelgid, n.d). An introduced, invasive species, it has no natural predators on the continent. Wooly adelgids are susceptible to cold temperatures and their reproduction can be slowed in cooler climates that reach -10 degrees or below (7 Facts About the Hemlock Woolly Adelgid, 2022). But in the Southern U.S., winters rarely reach single digits much less negative numbers. The defenses against this parasite are few, and it’s a plague that threatens to devastate a once plentiful tree and change the ecosystems around it forever.

“We can’t save them all, but we sure try.”

Katie Biggert is the Crew Lead of the Hemlock Wooly Adelgid Strike Team with the Tennessee Department of Forestry. It’s her expertise that we’re seeking today. Biggert’s full-time job is to crisscross the state, with a crew of seasonal field hands, to inoculate the Eastern Hemlock against a parasite that threatens to erase this native and majestic tree from Tennessee forests.

 “Hemlocks are special. They can’t be replaced by another species of tree, they’re one of a kind and once they’re gone they’re gone.” When I ask if they can protect all the hemlock trees, she laughs, “Our goal is to save 30% statewide…and that’s a stretch.”

Jed Grubbs, the Cumberland River Compact’s ILF Program Manager, measures an Eastern Hemlock tree to prepare the correct dosage of imidacloprid to protect against the wooly adelgid.

The inoculation process is simple and only takes a minute to apply and provides up to seven years of protection. When making site visits, our staff at the Cumberland River Compact adds support to help speed inoculation. A team of three people can protect nearly 75 trees in just a few hours. Most hemlocks are treated by pouring a measured amount of imidacloprid, a common insecticide, at the base of the trunk. Stands that are nearby to streams are injected directly with a trunk injection gun that delivers the insecticide directly to the tree’s vascular system. Interestingly, it is not the imidacloprid that kills the wooly adelgid parasite. It is chemically similar to a naturally occurring chemical called olefin found in Western Hemlocks (Hollowell, 2022b). The application stimulates the immune response and olefin production in our eastern trees, emulating the response of their western relative.

Grubbs muses on this difference while measuring hemlocks to calculate their correct dosage. “The Western Hemlock are protected already, they just know what to do. We’re not sure why our Eastern ones don’t automatically make the same chemical to ward off the adelgid, but at least we can help it get there.”

Our Water. Our Hemlocks.

The eastern hemlock is found from Nova Scotia to Minnesota, south through the Appalachian Mountains into Northern Alabama. A native species of North America, indigenous people used the bark to assist in the tanning of animal hides as well as for medicinal purposes (Eastern Hemlock – U.S. National Park Service). Sometimes called the redwoods of the east, these graceful trees can live for 800 years and provide the backdrop for many a serene setting for trout fishing and birdwatching.

Eastern Hemlock at the Fire Tower restoration site.

Hemlock habitat lends itself to providing the cooler waters needed to support trout populations. The root systems wind through streambanks providing stability and protection against erosion and flooding. As common streambank trees in the eastern United States, they are inextricably woven in with the health of the water. What happens in one area of the Cumberland River Basin impacts us all. The loss of Eastern Hemlocks is not just an issue for the surrounding habitat, but also for all of us downstream, every plant, animal, and person that depends on clean water from the Cumberland River.

Facts like these make the protection of the Eastern Hemlock seem not just important but critical to addressing water quality in our state. Biggert flips through pictures on her phone, taken at hemlock stands across the state. The pictures document the reality of inoculating versus not. The difference is stark; one is filled with fluffy green needles and tiny cones. The other is a skeleton of gray, a shriveled silhouette against a blue sky.

Restoring Streams with the In Lieu Fee Program

The Compact’s In Lieu Fee Program (ILF) pools funds from stream impacts and directs them towards high conservation value stream restoration projects across the Cumberland River Basin. In lieu fee, refers to the penalties the developers pay when construction impacts wetlands, streams, and habitat that have shaped Tennessee into one of the most biodiverse places on Earth. For every cedar grove dug up, wetland made into a field, or prairie paved over, state and federal laws require developers to pay for restoration. Instead of restoring small areas that won’t create sufficient habitat for wildlife to thrive, the Compact will accept a developer’s restoration obligations, pool these funds with funds from other developers, and locate large restoration projects in conservation priority areas. Priority areas are identified on their proximity to already restored and protected lands, occurrences of rare or endangered species, or ecologically important areas. 

Restored land is then permanently protected by conservation easements which prohibits development. By taking on large projects, the Compact is able to restore miles of connected streams and floodplains, and reestablish thriving habitat for native species and better protect our regions’ biodiversity.

How You Can Help

The Cumberland River basin is home to 3 million people and thousands of species and is one of the most biodiverse regions in the world.  Protecting and restoring the creeks, streams, and rivers of the basin is crucial to providing clean drinking water and thriving habitat for plants, animals, and people.

State parks located in impacted areas have gained support from friend groups to monitor the presence of and inoculate against the parasite. For individuals, a variety of methods to deter the spread of the wooly adelgid are outlined at

Making a one-time or recurring gift to the Cumberland River Compact helps to carry out stream restoration projects, wooly adelgid inoculation, and other water conservation initiatives across the Cumberland River Basin.

Author Bio

Meagan Hall

Meagan Hall is the Development and Communications Director at the Cumberland River Compact where she leads the Compact’s fundraising, marketing, and external communication initiatives. Meagan has a BFA in textiles from the Appalachian Center for Craft and a certificate in Nonprofit Fundraising from the University of Washington. She leads native and medicinal plant walks and teaches natural dye textile classes throughout Middle Tennessee.


7 facts about the hemlock woolly adelgid. (2022, June 16). Cary Institute of Ecosystem Studies.

Eastern Hemlock – Shenandoah National Park (U.S. National Park Service). (n.d.).

Hemlock Woolly adelgid. Tennessee State Government – (n.d.).

Hollowell, J. B. a. H. (2022b, February 16). How you can help the Eastern Hemlock.