Elms were once a staple of Minnesota’s tree canopy; this is how researchers hope to bring them back
The University of Minnesota is planting “survivor” trees in several places to help elms thrive after Dutch elm disease killed many of them.
Majestic elms towered above city sidewalks and filled out the canopy of dense Midwestern forests with their graceful, arching branches — until Dutch elm disease took them down by the millions.
Now, hopes of revitalizing the species are taking root across Minnesota. Most recently, hundreds of youths gathered Saturday in Bloomington to plant about 80 American elms, each just 6 or 7 feet high. The spindly trees are the pioneers that could spur a comeback, say University of Minnesota researchers.
“We would like to see elms restored to their prominent ecological role,” said Rob Venette, director of the Minnesota Invasive Terrestrial Plants and Pests Center at the University of Minnesota and a biologist with the U.S. Forest Service.
The American elm was an important component of wetland forests when Dutch elm disease arrived in the country, said Linda Haugen, plant pathologist for the U.S. Forest Service.
“It really roared through Minnesota probably in the ’70s and ’80s and we really noticed it in our cities and our towns,” Haugen said. “It killed a very high proportion of our American elms.”
In 1977, there were 1.3 million American elms with a diameter greater than 21 inches in Minnesota, Haugen said. Ninety-five percent of them are gone, leaving fewer than 60,000 big elms.
There are young American elm trees in forests today, but few larger than a foot in diameter. By that point they typically die from Dutch elm disease, she said.
The University of Minnesota Elm Selection Program is broader than Saturday’s event, which was notable because it was the project’s only public planting opportunity so far, said Ryan Murphy, a researcher in the department of forest resources at the university.
Nora Kelly, 6, helps fill dirt around a tree that was planted Saturday in Bloomington. Alex Kormann, Star Tribune
The project, which began the early 2000s, was among the first large-scale efforts to work with “survivor elms” in Minnesota, Murphy said. Most of its trees have survived the planting process.
Haugen said both the university and the Forest Service, which has elm revitalization projects elsewhere, are trying to find more varieties of disease-resistant elm and sometimes collaborate.
The Minnesota project, funded through the Environment and Natural Resources Trust Fund and the Minnesota Turf and Grounds Foundation, has planted over 200 disease-resistant elms, Murphy said. Those trees are spread across several sites, including Nerstrand Big Woods State Park, Elm Creek Park Reserve in the northwest metro and the Minnesota Landscape Arboretum in Chanhassen.
The question, though, is whether the trees will resist Dutch elm disease long-term.
Graham Bennett places an elm tree into a hole as part of a tree planting event.Alex Kormann, Star Tribune
‘Survivor elms’ take the lead
It’s not clear how Dutch elm Disease came to the United States, Venette said, but it probably arrived in “some sort of infested wood material.” The disease is caused by a fungus, and spreads when people move wood or bark beetles carry it to a new area.
The disease didn’t kill every American elm — it “left behind some survivors,” Venette said, and those became the basis of the project.
Those hardy trees are being used to grow the next generation, Murphy said.
First, someone identifies a “survivor” elm tree, one that was thriving despite other elms’ death. It might be in someone’s yard or a park, he said.
Cuttings from that tree are grafted to a seedling elm and then grown in the nursery. Once they are big enough, the researchers infect the trees with Dutch elm disease fungus and wait to see whether they’re actually disease-resistant or just survived by luck. Many die, he said.
The ones that live are planted as part of the project.
Venette said the project’s end goal is to diversify Minnesota forests, an effort that has taken on more urgency as the state loses so many ash trees to the Emerald Ash Borer, he said.
A map marks the locations where oak and elm trees will be planted on a Nature Hiking Trail leading to the Minnesota River in Bloomington. Alex Kormann, Star Tribune
“We also care about it in light of climate change,” Venette said. “This is a really nice way to sequester carbon.”
Saturday’s tree planting event also gave young people the opportunity to do conservation work. Teens from the Green Crew, the youth program of the Izaak Walton League’s Minnesota Valley chapter, spent more than six months organizing the tree planting and a Native American-led blessing of the land.
They partnered with U researchers and learned best practices for tree planting and care, secured the support of sponsors and recruited hundreds of community volunteers, including from eight high schools and several Boy Scout units.
“I heard all these stories about big trees … that used to cover the streets in arcs and I wanted them back,” said Hannah Barisonzi, the Green Crew’s co-founder and a freshman at the Blake School, who led the tree planting for an Eagle Scout project.
While the Green Crew used wheelbarrows to transport their elms, younger kids had the chance to plant oak saplings and pollinator plants.
Members of the Green Crew will help researchers care for the new elm trees over time.
“This is about restoring the Earth,” Barisonzi said.
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