Hunting for Hemlocks

Ken Donny-Clark spent his last semester at UNC-Chapel Hill in the woods searching for a dwindling population of trees that local wildlife depends on: Carolina hemlocks.

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January 20th, 2023

“It’s just a little further,” Ken Donny-Clark promises.

The UNC-Chapel Hill senior crawls on his hands and knees, pushing aside branches and small plants as he squeezes his way to his destination. After a few more minutes of struggling through the brush, he gets to a spot where he can stand. Leaves crackle as he continues to navigate the sun-dappled woods. Eventually, he stops in front of a scrawny, lightly colored evergreen: a Carolina hemlock.

From his multi-pocketed, olive-green military jacket, he spills a multitude of tools onto the forest floor — including a large orange measuring tape, over a dozen white straws, Sharpies, and a yellow waterproof notebook — and gets to work. He presses a straw-sized, T-shaped hollow tube with an auger into the tree in front of him and begins to crank it into the bark.

Thwock, thwock, thwock.

In minutes, he’s driven the increment borer through the tree to the other side. He slides the extractor into the hollow tube, and when he pulls it back out, a cream-colored core comes out.

“That’s a good one,” he says.

This isn’t Donny-Clark’s first rodeo. He’s been at this all semester for a research project he’s working on at the UNC Institute for the Environment’s Highlands Field Site in Western North Carolina.

The trees he’s studying are Carolina hemlocks, which grow in small, isolated patches along rocky hillsides, cliffs, and ridges throughout the southern Appalachian Mountains. Considered a foundation species, these conifers create a unique shade environment and soil chemistry that some organisms thrive in. Their numbers are dwindling because of the hemlock wooly adelgid, an invasive insect from East Asia that eats the inside of the trees and injects a toxin that makes the needles fall off. Infested trees often die within four years.

This makes Carolina hemlocks difficult to find — and a great study subject for Donny-Clark. Little data has been collected for the trees, and that’s precisely what is needed to help conserve the remaining population.

The core of conservation

In partnership with the Highlands Biological Station and with permission from the U.S. Forest Service and private landowners, Donny-Clark spent the Fall 2022 semester searching for Carolina hemlocks along Laurel Knob — the tallest continuous cliff face in the eastern United States, towering at 1,200 feet. Overall, he found more than 30 Carolina hemlocks on the rocky outcropping. But it wasn’t easy.

“There’s a lot of bushwhacking involved,” he says with a laugh. “But I feel like I’ve really earned the data once I’ve gotten it.”

When sampling trees, Donny-Clark removes two cores from each one — a minimally invasive process that does little damage.

“If you don’t remove the core fast enough, the tree will actually start to fill the hole, making the borer hard to remove,” he says.

Along with the cores he takes a series of measurements: the direction he’s facing when he collects the core, the width of the tree, and the height from the ground to the core site. Then he returns to the lab, where he dries the cores before putting them under a microscope to reconstruct them like a jigsaw puzzle, because most fall apart during the extraction process.

After a core has been rebuilt, Donny-Clark heads to the maintenance shed to sand it down, which helps him identify the rings. Using a software called CooRecorder, he measures the width of individual rings to build a history for that tree. Tree rings not only inform researchers about the age of a tree, but the weather patterns that existed as it grew — a field called dendrochronology.

Then, he uploads it into an online database so other researchers can access it.

“We don’t really know much about the growth of Carolina hemlocks and how they’re influenced by climate, so that’s what we’re trying to figure out here,” Donny-Clark says.

Finding the optimal climates for these trees to grow can aid conservation efforts by providing the best locations for planting trees to help restore the population.

A semester at altitude

Each year, a small cohort of students are selected to spend an entire semester at the Highlands Field Site, located in the mountain town of Highlands, which sits at 4,118 feet above sea level. In just 15 weeks, they learn about the scientific method, apply it to a research project, and produce an academic paper on the topic.

“Providing this opportunity is a great way to help students learn what they’re interested in or what they might not be interested in and get them excited as well,” says Rada Petric, director of the field site.

For the hemlock project, Donny-Clark was paired with two mentors — Chris Oishi, a research ecologist with the U.S. Forest Service, and Joel Scott, a biological sciences technician at the Coweeta Hydrologic Laboratory — who taught him how to core trees, process the samples, and upload that data into an online repository.

“I added an extra semester just to be here,” says Donny-Clark, who was originally supposed to graduate in May 2022.

Even though he’s graduating a semester late, Donny-Clark is just 18 years old. He began taking college courses at Durham Technical Community College when he was 14. The oldest of six kids, his parents homeschooled him and felt it prudent to jumpstart his college education.

While he’s not sure what his next steps are yet, his semester in Highlands ignited a passion for research and working outdoors.

“I’ve enjoyed all the hands-on experience I’ve gained and meeting the people who live here and are experts in their own field,” he says. “I’ve made a lot of connections and learned a lot about what the real working environment looks like for an ecologist.”

Ken Donny-Clark is a senior majoring in environmental science and minoring in biology within the UNC College of Arts & Sciences.

Rada Petric is the director of the Highlands Field Site and a research assistant professor at the UNC Institute for the Environment.