Scientists use disease to restore iconic American elm trees

The fungal pathogen that decimated millions of American elms across the U.S. is now being used to restore the iconic species.In Vermont, Leila Wilson, a research ecologist with the U.S. Forest Service, is among the scientists leading an effort to overcome Dutch elm disease, which has killed tens of millions of elm trees over the last century. Scientists with the Forest Service and The Nature Conservancy Vermont spent the summer injecting 6,000 young elms with Dutch elm disease spores to evaluate their resistance.The surviving saplings will go to a breeding program designed to expand the genetic diversity of disease-tolerant elms, with the goal of eventually using them for restoration across forests, riverbanks, and yards."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 fungal pathogen that decimated millions of American elms across the U.S. is now being used to restore the iconic species (AP Photo/Robert F. Bukaty)The young elms were bred from a group of several dozen Northeast trees that survived Dutch elm disease, a fungus introduced to the U.S. nearly a century ago. Spread by bark beetles, the pathogen blocks water transport in trees, causing them to starve. This disease is the primary reason elms exceeding 70 feet (21 meters) in height are far less common in New England today than in past generations.The initiative to protect elms forms part of a broader national push to curb forest pests and diseases that jeopardize longstanding industries like logging and endanger delicate ecosystems.Preserving American elms is critical to climate change efforts because they strongly affect the hydrology of surrounding ecosystems, explained Kathleen Knight, a Forest Service research ecologist based in Ohio. This role is especially vital during an era of changing weather, when unpredictable droughts and flood events threaten forest lands.Elms are particularly vital in wet forest regions, Knight noted. They tolerate standing floodwaters, withstand harsh northern winters, and absorb excess rainfall like a sponge to help prevent devastating flood damage along river networks."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.The elm also holds deep cultural significance in the Northeast, said Gus Goodwin, a senior conservation planner for The Nature Conservancy. Although elms grow throughout many parts of the country, they were once a ubiquitous feature in New England towns, making their loss deeply felt across local 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."A different type of injection treatment is being deployed to preserve another prized species: the ash tree. Ash populations have experienced severe losses due to the emerald ash borer, a destructive beetle responsible for killing millions of trees since arriving in the U.S. in the early 2000s.In response, the Appalachian Trail Conservancy is treating select ash trees with insecticide injections to improve their survival chances. The organization reports treating approximately 1,400 ash trees along trail segments in North Carolina, Tennessee, Georgia, and Massachusetts since 2016."Being able to see where there are ash trees that are still standing and they are healthy, and they are a major component of the forest, supporting the biodiversity that's here, is really awesome," said Emily Powell, southern non-native invasive species coordinator for the conservancy.The ash initiative differs from the elm program because the elm project centers on selective breeding rather than ongoing chemical treatments.In flood-prone Montpelier, Vermont, city arborist Joseph Ferris stands beside a grand elm tree that has stood in the state capital since the late 1800s."It’s a really lovely reminder of what’s possible for urban trees," he said.As someone whose career is centered on addressing forest threats, Ferris is encouraged by the prospect of a new generation of Dutch elm-resistant trees."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," he 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."