U of M researchers are planting ‘survivor' trees in hopes of defeating Dutch elm disease

Yahoo

7 days ago

The 36 trees planted last week at Boutwells Landing senior living community in Oak Park Heights have a big job: To help revitalize the state's elm population.
The American elm trees, each about 2 years old and 4 to 6 feet tall, were cloned by University of Minnesota researchers to be resistant to Dutch elm disease, a fungal disease that killed millions of elm trees around the world.
In the late 1970s, there were 1.3 million American elms with diameters greater than 21 inches in Minnesota. Dutch elm disease killed 95 percent of them, leaving behind fewer than 60,000 big elms, according to U researchers.
Ryan Murphy and Ben Held, co-investigators on the U's disease-resistant elm selection and reintroduction program, want to revive the population. On May 16, they got some help from Boutwells Landing residents David Lime, 84, and Neal Kingsley, 87, both U.S. Forest Service veterans, who participated in the three-hour planting project.
Soon after Lime moved to Boutwells Landing three years ago, he pitched the idea of starting a nursery in the southeast corner of the 100-acre property to help offset the loss of ash trees from emerald ash borer.
Boutwells Landing officials expressed interest, and Lime, who worked for 20 years in the Forest Service's experiment station on the St. Paul campus and later taught at the U's College of Forestry, started looking for places giving away trees and people who were researching trees 'where we could invite them to plant some trees on our property,' he said.
Lime connected with Kingsley, and the two met with Rob Venette, director of the Minnesota Invasive Terrestrial Plants and Pests Center at the U of M and research biologist with the U.S. Forest Service Northern Research Station. He connected them with Murphy and Held.
'It was just one of those things where they had space, and we were looking for places, and it just was the right connection,' Murphy said.
Dutch elm disease is caused by a fungus that can be spread by a bark beetle or through two trees that have interconnected roots. Beetles reared in infected trees emerge from the diseased wood carrying spores, which they then deposit into healthy trees by feeding on the young twigs. The fungus triggers reactions that block the tree's vascular system, which prevents it from getting water and nutrients normally, and it becomes wilted, leading to rapid death, Murphy said.
Fortunately, Dutch elm disease didn't kill every elm tree in the state. Some very hardy 'survivor' elms were left behind.
'Oftentimes, they're the only elm tree left in an area where everything else has died,' Murphy said.
Said Venette: 'It's just a matter of a random mutation that happens to occur in these trees. In general, the species as a whole is highly susceptible, but it's just these very lucky individual (trees) that have natural resistance.'
Researchers are using the 'survivor' elms from around the state – identified by forestry officials, arborists and private landowners – to grow Dutch elm disease-resistant trees.
Here's how it works: Researchers visit the 'survivor' elm in the wintertime and take the branch tips and then grow a tree genetically identical to that elm. 'You take that tissue from that twig, and you graft it onto a rootstock,' said Murphy, who also manages the U of M's Urban Forestry Outreach & Research Lab, which provides education about trees to communities around the state.
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The cloned trees are then planted back in the landscape either at the St. Paul campus or at the Minnesota Landscape Arboretum in Chanhassen 'to confirm that they really are resistant, and that they weren't just lucky and got missed by the bark beetles,' Venette said.
Once the tree is propagated, it can take five to seven years to get to a size where it can be inoculated with the pathogen, Murphy said.
'We then drill a hole into the main stem of the tree, inject the tree with concentrated spores of the fungus which causes the disease, and wait to see its effect,' he said. 'To find one resistant cultivar, it could easily take 10 years.'
If the tree survives inoculation with the fungus, researchers will then propagate more of them and plant those at different test sites around the state 'because we have more evidence to suggest that they are truly resistant,' he said.
The resistant elms are being planted at Boutwells Landing, Nerstrand Big Woods State Park, Elm Creek Park Reserve and in the Minnesota River Valley.
Researchers plan yearly follow-up visits to assess the tree performance; the trees are expected to grow several feet each year, Murphy said.
Fifteen more trees will be planted in a forested area at Boutwells Landing that was impacted by emerald ash borer, an invasive beetle that attacks and kills ash trees. Ash trees were planted in many urban forests in Minnesota to replace elm trees decimated by Dutch elm disease, Venette said.
'It's all part of growing a more diversified urban forest,' he said. 'We've nearly come full circle.'
The research project at Boutwells Landing is expected to last somewhere between five and 10 years 'because we really are trying to understand how well these trees get established and what factors might be affecting their survival and growth,' Venette said.
The $226,000 research project, funded by the Minnesota Invasive Terrestrial Plants and Pests Center, started in January 2024. An earlier U of M research project on developing Dutch-elm resistant trees received $234,000 in funding from the center and was completed in 2023. The center was formed in 2014 to coordinate the U's research into invasive insects and land-based plants. It is funded by the state's Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources. The center, which has four employees, has an annual budget of $330,000.
Officials were thrilled when Murphy and Held proposed the project, said Heather Koop, the Invasive Terrestrial Plants and Pests Center's associate program director.
'When we can get a piece of research to that point of implementation, that's the gold standard for us … that's how we really like to measure our success,' she said. 'So often we see research that is done that never really gets to that next stage. Because this is all publicly funded, we feel very strongly that this research needs to be in the public realm, and people need to understand it and how to use it. Hopefully, they'll apply it, and hopefully, we'll see better management options available for different invasive species.'
Another plus: The project 'engages people in science,' she said. 'You have these folks who are super-eager to help us out, and that just makes me really happy.'
In addition to having a few retired foresters, Boutwells Landing has 'a very rich community of folks who are interested in science,' Venette said. 'They reached out and asked about opportunities to engage in collaborative work related to trees, and we just happen to have this project that was a nice fit.'
Researchers worked with teens from the Green Crew, the youth program of the Izaak Walton League's Minnesota Valley chapter, to plant trees in Bloomington on Earth Day 2023, so it was fitting to work with seniors on the Boutwells Landing project, Venette said. 'It really shows the breadth of interest in this kind of work,' he said.
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Lime, who walks or drives past the new trees at least once a day, said the project is giving staff and residents at Boutwells Landing a chance 'to learn about the role of science in helping solve serious natural-resource problems' and how they can help bring American elm trees back to the Minnesota and Upper Midwest landscape, he said.
'The idea is that if we can re-establish them in Minnesota, maybe we can do it in other states,' Kingsley said. 'Bringing them back would be great because they were beautiful.'
Although Kingsley knows he may not be around to see whether the experiment was a success, he said he is happy to have played a part.
'My grandfather built fishing schooners, and I remember as a kid growing up seeing a ship that my grandfather helped build,' he said. 'It was nice. Maybe my grandkids or great-grandkids will say, 'See that tree? Bamp helped plant that.' That would be kind of nice.'