Scientists use Dutch elm disease to breed resistant trees for restoration

MONTPELIER, Vt. -- The very disease that has decimated millions of American elms in the U.S. is now being used to bring the iconic trees back.

In Vermont, Leila Wilson, a research ecologist with the U.S. Forest Service, is one of the scientists leading an effort to beat 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 elm trees with Dutch elm disease spores to test their resistance to the disease.

The survivors will be sent to a breeding program with a goal of growing the genetic diversity of disease-tolerant elm trees. They will one day be used for restoration in forests, riverbanks and backyards.

“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 were bred from a group of a few dozen trees in the Northeast that have survived Dutch elm disease, which is a fungus that arrived in the U.S. a little less than a century ago. The fungus, spread by bark beetles, stops trees from being able to drink water, which makes them starve. The disease is a key reason towering elm trees of more than 70 feet (21 meters) are less common in New England today than they were generations ago.

The drive to save elm trees is part of a broader fight in the U.S. to try to beat back forest pests and diseases, which threaten longstanding industries such as logging and damage some of the nation's most fragile ecosystems.

One of the reasons protecting American elm trees is so important is because they have a huge impact on the hydrology of their surrounding ecosystems, said Kathleen Knight, a research ecologist with the Forest Service based in Ohio. That is especially important in the era of climate change, when unpredictable weather and periods of flooding and drought can impact forests.

The trees are especially important in wet forest areas, Knight said. They tolerate flooding, they can live through the cold winters of the north, and they have the ability to act like a sponge after rainfall and help prevent flooding that can be catastrophic to river systems, she said.

“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 is also culturally important to the Northeast, said Gus Goodwin, a senior conservation planner for The Nature Conservancy. Though elm trees live in many parts of the U.S., they are a “ubiquitous part of the landscape” in New England towns, and the loss of the trees over the years has been devastating in those communities, he said.

“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.”

Ash trees are another species that has succumbed to a devastating infestation — emerald ash borer, a beetle that has killed millions of the trees since arriving in the U.S. in the early 2000s.

But the Appalachian Trail Conservancy is fighting back by injecting some ash trees with an insecticide to give them a chance at survival. The group said it has treated about 1,400 ash trees along the trail 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 campaign differs from the push to save elm trees because the elm drive is a breeding program rather than an inoculation effort.

In Montpelier, Vermont, a city that has experienced significant flooding through the years, arborist Joseph Ferris stands next to a giant elm tree that has stood in the state’s capital since the late 1800s.

“It’s a really lovely reminder of what’s possible for urban trees,” he said.

As someone who spends his professional life focused on the challenges forests are facing, Ferris is excited about 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.”

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Whittle reported from Portland, Maine.