Power Line Rights-of-Way: A Haven for Disappearing Grassland Ecosystems?

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By Michael Matz

In the U.S. Southeast, preliminary results of EPRI field studies with Southern Company and the Tennessee Valley Authority (TVA) indicate that well-managed power line rights-of-way (ROWs) can increase biodiversity and conserve fragile grassland ecosystems.

Throughout the United States, development and urbanization have nearly eliminated grassland ecosystems. In the Southeast, the roughly 120 million acres of grasslands believed to exist at the time of European settlement have declined by more than 90% as a result of habitat loss and fragmentation.* Many ecologists believe that it is important to conserve the grassland remnants because they contain a large portion of the region’s biodiversity.

Many utilities use integrated vegetation management (IVM) on ROWs to remove tree sprouts and other woody vegetation that can damage power lines. (To learn more about IVM, see this fact sheet and these additional resources from the U.S. Environmental Protection Agency.) IVM often includes planting native vegetation, periodic mowing, and herbicide applications. If properly managed, ROWs can mimic natural grasslands and serve as ‘surrogate’ habitats for forbs, grasses, and other flowering grassland plants. This in turn can promote abundance and diversity of bees and other insect pollinators. In field tests with utilities, EPRI is examining how vegetation management strategies can suppress trees and invasive plants while supporting native plants and pollinators.

Central Alabama: Exploring the Relationship Between IVM and Biodiversity

Southern Company, its subsidiary Alabama Power, Auburn University, and EPRI are collaborating on a field study in central Alabama, with two main objectives:

• Quantify the biodiversity of flowering plants and insect pollinators on ROWs
• Evaluate the effects of commonly used IVM practices on this biodiversity

Between May and October 2018, researchers conducted baseline surveys of plants and insect pollinators on four ROWs and adjacent forests. Two key findings:

• Of the 41 flowering plant species observed, 40 were in the ROWs and 4 in the adjacent forests.
• Of the 71 bee species observed, 68 were in the ROWs and 29 in the adjacent forests.

“The greater number of plants and bees in the ROWs compared to the forest indicates that the ROWs are supporting biodiversity,” said Ashley Bennett, an EPRI entomologist leading the field research.

In June 2019, researchers applied three IVM treatments on different ROW plots:

• T1: A sprayer mounted on an all-terrain vehicle applied a large volume of a broad-spectrum herbicide (a chemical that controls a wide array of grasses and broadleaf plants) throughout the entire plot.
• T2: Researchers manually sprayed small volumes of the same broad-spectrum herbicide on tree sprouts and invasive species. The remainder of the plot was not sprayed.
• T3: Researchers manually sprayed small volumes of a grass-friendly herbicide (a chemical that controls a wide array of broadleaf plants but not grasses) on tree sprouts and invasive species. The remainder of the plot was not sprayed.

Between June and October 2019, researchers surveyed plants and pollinating insects monthly. As of August 2019, they found that forb abundance remained the same in plots treated with T2, declined by 71% in plots treated with T1, and declined by 45% in plots treated with T3. Post-treatment bee abundance was the same for T1, T2, and T3.

“The fact that we found significantly more forbs with T2—the selective spraying of the broad-spectrum herbicide—suggests that targeted application on tree sprouts and invasive species can protect non-targeted plants like forbs,” said Bennett. “It’s not clear why we did not see the same positive effect on forbs in T3—the treatment where we selectively sprayed with the grass-friendly herbicide. These results are from the first growing season after treatments were applied. Because it can take several years for plants and pollinators to respond to vegetation management, we plan to monitor the plots until 2022.”

“Through this multi-year research project, Southern Company hopes to inform ROW vegetation management practices while advancing pollinator conservation,” said Claire Ike, a Southern Company senior environmental specialist who is leading the research. “The research is one example of the commitment of Southern Company and our subsidiaries to natural resource conservation in the communities we are privileged to serve and also call home.”

“Alabama Power is encouraged with the initial findings from this project,” said John Morris, arborist supervisor at Alabama Power. “We share a common view that herbicides are an effective tool for IVM. Through this research, we hope to better understand herbicide products and application methods that not only achieve operational goals, but also increase and improve pollinator habitat.”

Cumberland Plateau: Plant and Pollinator Surveys

Nearly all the grasslands and savannas that once dominated the Cumberland Plateau region—which spans eastern Kentucky, eastern Tennessee, and parts of northern Alabama and Georgia—have been lost to forest encroachment and development over the last 200 years. TVA’s power line ROW network is preserving remnants of this ecosystem.

“We have found many populations of rare plant species on TVA’s ROWs on the Cumberland Plateau and have come to understand these habitats as regionally important for plant conservation,” said Adam Dattilo, a botanist at TVA. “With the emergence of the global pollinator crisis, I began wondering if TVA’s standard vegetation management practices benefit pollinators in addition to helping plants.”

Similar to the T2 treatment in the Southern Company study, TVA’s vegetation management teams manually and selectively apply small amounts of herbicide to woody species that could damage power lines. TVA is collaborating with Southeastern Grasslands Initiative (based at Austin Peay State University), the Mississippi Entomological Museum, and EPRI to examine the extent to which this approach can support conservation of grassland biodiversity.

Researchers designed a three-year study to compare plant and pollinator biodiversity in 15 ROW sites with that of 15 adjacent forest sites. In 2019, they surveyed plots (17 meters by 17 meters) on 5 ROW and 5 forest sites. Preliminary results:

• ROW plots had between 118 and 131 plant species—or an average of 2.5 times the number of plant species as adjacent forest plots.
• Four orchid species were found in ROW plots.
• Pan traps in ROW plots caught an average of 16.1 times more bees than pan traps in forest plots.
• Timed net sampling yielded an average of 13.8 times more bees in ROW plots than in forest plots.

“Similar to the data from our ROW research with Southern Company in central Alabama, these data show that TVA’s ROWs have much greater biodiversity than the surrounding forest, suggesting that vegetation management practices are protecting native plants and pollinators,” said Bennett. “In addition, many of the species we’re finding are not weedy species. They’re indicative of high-quality grassland remnants.”

Over the next several years, researchers plan to survey plant and pollinator communities on 10 additional ROW plots and 10 adjacent forest plots.

“Ultimately, these results will help us better communicate the environmental benefits of the TVA ROW vegetation management program to the general public,” said Dattilo. “Perhaps more importantly, from a conservation perspective, this project will illustrate the urgent need for grassland restoration on larger tracts of land outside of TVA’s ROWs to conserve pollinator and plant biodiversity into the future.”

*References:

• Estes, D., M. Brock, M. Homoya, and A. Dattilo. A Guide to the Grasslands of the Mid-South. Published by the Natural Resources Conservation Service, Tennessee Valley Authority, Austin Peay State University and the Botanical Research Institute of Texas. 2016.
• Estes, D. and T. Witsell. The Southeastern Grasslands Initiative. Published by Austin Peay State University. 2017.

Photo at top of article: A Rose Pogonia Orchid on a TVA right-of-way. Photo courtesy of Theo Witsell.