In a novel approach to combat Dutch elm disease, scientists are intentionally exposing young elm trees to the very fungus that has killed millions of their predecessors. This initiative, led by researchers from the U.S. Forest Service and The Nature Conservancy in Vermont, aims to identify and cultivate disease-resistant American elms.
Over the summer, approximately 6,000 young elm trees were injected with Dutch elm disease spores. The survivors of this trial will be selected for a breeding program, with the ultimate goal of creating a diverse population of disease-tolerant elms. These trees are intended for future restoration projects along riverbanks, in forests, and in urban landscapes.
Leila Wilson, a research ecologist with the U.S. Forest Service, explained that the surviving trees will be moved to a seed orchard. "We will put those newly propagated trees into a seed orchard, basically just a big fenced area, will grow and love those trees for about 15 or so years, at which point they should produce seeds, and that seed can be used for restoration," Wilson said.
The young elms used in the experiment were bred from a limited number of trees found in the Northeast that have demonstrated natural resistance to Dutch elm disease. The fungus, which arrived in the U.S. nearly a century ago and is spread by bark beetles, obstructs the trees' water uptake, leading to starvation. This disease has significantly reduced the prevalence of mature, towering elm trees in regions like New England.
This effort is part of a broader national strategy to counter the impact of forest pests and diseases that threaten key industries like logging and jeopardize fragile ecosystems. Kathleen Knight, a research ecologist with the Forest Service, highlighted the significant role American elms play in the hydrology of their surrounding environments. This ecological function is particularly crucial in the context of climate change, which brings unpredictable weather patterns, including periods of flood and drought.
Elm trees are especially vital in wet forest areas, Knight noted. They can tolerate flooding, survive cold northern winters, and act as natural sponges to mitigate floodwaters, thereby preventing damage to river systems. "And these invasive pests and pathogens have been having a huge impact on these tree species. And we're just trying to get those species back to the role they previously played in these systems," Knight said.
Culturally, the elm holds importance in the Northeast. Gus Goodwin, a senior conservation planner for The Nature Conservancy, described the elm as a "ubiquitous part of the landscape" in New England towns, and its decline has been deeply felt in these communities. "And what's missing is the big trees," Goodwin said. "A lot of people remember losing the elm. From their childhood home, their school yard. There's this kind of gravitational pull toward the elm and its loss."
American elms are not the only tree species facing significant threats. Ash trees have been decimated by the emerald ash borer, an invasive beetle that arrived in the U.S. in the early 2000s. In response, the Appalachian Trail Conservancy has been treating approximately 1,400 ash trees along the trail in several states with an insecticide since 2016.
While the ash tree preservation efforts involve direct treatment, the initiative to save American elms focuses on a long-term breeding program to foster genetic resistance. Arborist Joseph Ferris in Montpelier, Vermont, expressed optimism about the potential for a new generation of disease-resistant elms. "It's a ray of hope that is hard to feel when we're walking through a forest and seeing all these infestations and damage," Ferris said. "I would love to see American elm resistant, available not for just our urban plantings but restoring plantings along our streets and along our riverbanks, and just boosting the regional genetic resistance."