The discovery of an adult beetle suggests that the forest is in the early stages of infestation by the invasive species.
The emerald ash borer (EAB), a beetle native to northeastern Asia that infects and kills all species of North American ash, is now present at the Hubbard Brook Experimental Forest.
John Deitsch, a rising senior at Cornell University who is spending the summer at Hubbard Brook with the Cornell Lab of Ornithology’s Hubbard Brook Field Ornithology Program, discovered an individual EAB in an insect trap on a research plot sampled on June 18. Bill Davidson, a forest health specialist with the New Hampshire Division of Forest and Lands, confirmed the identification. The finding makes Hubbard Brook the farthest north that EAB has been detected in New Hampshire by about seven miles.
The discovery of an adult beetle within the forest suggests that Hubbard Brook is currently in the early stages of infestation, Davidson says. Adult EAB females lay their eggs beneath the ash tree's outer bark. Larvae tunnel and feed on the inner bark, destroying xylem and phloem tissue and disrupting the tree's ability to transport food and water, eventually killing it. Davidson expects more noticeable signs of EAB—such as thinning foliage, woodpecker damage, and insect exit holes—to become evident within one to two years, while significant tree dieback is likely within three to four years.
The potential impact of the unfolding invasion is immense. “This is a perturbation on the scale of the biggest experimental manipulations that have been done at Hubbard Brook,” says Matt Ayres, a professor of biological sciences at Dartmouth College and a Hubbard Brook Investigator. “And we’ve done some pretty big ones.”
The Hubbard Brook Valley is home to approximately 26,000 ash trees—almost all of them white ash, Fraxinus americana—according to data collected by the vegetation crew. Based on the impacts of EAB in other forests, the mortality rate for the ash trees at Hubbard Brook is expected to be total or near total.
EAB was first discovered in North America in 2002 in southeastern Michigan and has since spread to 35 U.S. states and five Canadian provinces. New Hampshire first documented the insect in 2013; it is now present in nine of the state’s 10 counties, with Coos County being the only exception. The timing of the EAB finding at Hubbard Brook aligns with researchers’ predictions for the rate of spread. “It was absolutely inevitable,” Ayres says.
Hubbard Brook researchers have been busy preparing for exactly this inevitability. While EAB’s relentless attack on ash is certain to cause significant cultural and economic impacts—particularly for Indigenous groups that rely on black ash for basket weaving—at Hubbard Brook the focus is on the disruption to the forest ecosystem.
Liz Studer, a PhD Candidate in the Ayres Lab at Dartmouth College, has been studying the ecological role white ash plays in the forest pre-invasion in an effort to understand what the consequences will be once it’s lost. Studer’s research examines ash’s relationship with birds, microfauna, other plants, fungi, and more. When EAB kills the white ash at Hubbard Brook, it will likely be replaced by a combination of American beech, yellow birch, and sugar maple. Some ecosystem dynamics may be drastically impacted by this change in species composition, while others may see very little effect.
For example, Studer has found that spring ephemerals like trilliums favor the habitat beneath white ash. During the growing season, ash trees put their leaves out several days later than other species. This leaf-out delay creates gaps in the canopy where light can penetrate through to the forest floor. For plants like spring ephemerals, whose above-ground life cycle lasts only a matter of weeks, a few extra days of good sunlight can make all the difference.
Now that EAB is confirmed at Hubbard Brook, researchers are quickly moving forward with discussions with state officials on whether to experimentally protect a number of ash groves in the forest using the insecticide emamectin benzoate. Much of the on-the-ground management, including dealing with trees that die and become hazardous to researchers working in the forest, will fall to Ian Halm, Hubbard Brook’s site manager. “I have to make sure we come up with a well thought out plan to move forward,” Halm says.
Whatever happens, Hubbard Brook researchers plan to collect significant data on EAB invasion. “Our job is to learn as much as we can. We have the benefit of foresight,” Ayres says. “Other places where it’s already invaded, it all happened so fast that the research studies have been very limited in what they could do. Our baseline data will be unique.”
Making the discovery early in the infestation means the community is well positioned to take action.
“It’s tremendously valuable to us that we’ve made that discovery,” Ayres says, “ and it’s not the least bit surprising that it was an undergraduate that did it. It was not the research objective, but you do good field biology and you learn things—and sometimes the most interesting things that you learn aren’t exactly the answer to the question that you started with. Kudos to John Deitsch and his sharp eyes and good research skills.”