Courtesy Photo | Sara Rother, U.S. Army Corps of Engineers, St. Paul District forester, uses a...... read more read more
The St. Paul District, in collaboration with the U.S. Forest Service and U.S. Fish and Wildlife Service, is actively working to rehabilitate floodplain forests, and one of the strategies is the restoration of American elm to its historic role, through selective breeding for Dutch elm disease resistance.
Between Pool 4 and Pool 9, the St. Paul District is collecting American elm twig samples from trees that have survived multiple waves of Dutch elm disease.
“The idea is to graft and grow those samples, multiply by cuttings and then test for resistance to Dutch elm disease,” said Andy Meier, lead forester for the district’s environmental section.
Foresters plan to plant the rooted cuttings produced from the grafted twigs at a site in Pool 8, where they can evaluate their resistance to Dutch elm disease. Any trees that show resistance will be retained on the site to produce seed for future planting efforts within the Mississippi River floodplain and beyond.
“This partnership benefits us, but ultimately it benefits the nation as a whole because these disease-resistant trees are available to the public,” Meier said. “You can buy elm trees from a landscape nursey that are disease resistant, but they are from 3-4 clones that are limited in their genetics and almost all of them are from out east. We’re working to create more genetic diversity in the disease-resistance trees.”
The partnership is important because neither the Corps, nor the U.S. Fish and Wildlife Service have the specific expertise that the U.S. Forest Service brings to the table for plant health and plant pathology, Meier explained.
“We could go out and collect seeds from these trees and send them to a nursery, but we don’t have the capacity to evaluate whether what we’re doing has any benefit, and we may not be able to tell for 50 years,” he said. “Bringing in the Forest Service allows us to evaluate that much more quickly.”
Comparing the amount of forest in the floodplain now to the amount of forest that was there at the time of European settlement, in many areas, 50% or more of the historic forest cover has been lost and continues to be lost at a rate of about 2-3% every 10 years, Meier said. The floodplain forest is one of the most imperiled habitat types on the Mississippi River.
Most of the tree samples were taken in Pool 9. “Pool 9 is a hot spot for surviving elms,” he said. “More than half of the samples were from there. If you look at American elms across the United States, I think some of the twigs that we collected are from some of the biggest elm trees on the landscape.”
The process of collecting the samples includes using a rope saw, which Meier describes as being a little chainsaw blade that attaches to two ends of the rope and pulling that to the top of the tree while it’s dormant to saw off a small twig – a diameter smaller than a finger.
After the samples were taken, they were sent to the Forest Service’s Northern Research Station in St. Paul, Minnesota, where they were grafted onto elm seedlings in a greenhouse.
“We have shoots leafing out of the grafts,” said Melanie Moore, biological technician with the Forest Service, Northern Research Station. “We’ll wait until there’s substantial growth, cut them up, apply rooting hormone and put in the mist to produce roots, pot them up and grow. The resultant trees are essentially clones of the parent tree.”
The trees will then grow for 1-2 years, and then a subset of those will be replanted in Pool 8 in a seed orchard. The Pool 8 location was chosen for its proximity to the Corps’ La Crescent field office because it will require more proactive management and maintenance than a normal planting.
“We’ll then test to determine if any of those trees have resistance,” Meier said. “Ultimately, we hope to be able to plant those resistant trees back into the floodplain forest and restore the original component of the landscape to a certain extent.” He added that ideally in 30-50 years, those resistant trees will start to grow and produce seed naturally to pollinate other trees and increase the resistance of the natural population.
Moore said that the Northern Research Station has developed an inoculation test whereby they inject the trees with spores of the Dutch Elm Disease fungus and rate the response over time.
“One of the biggest issues that we have with floodplain forests on the Upper Mississippi River right now, is that we have very low species diversity,” Meier said. “The species that can grow in the floodplain have to be tolerant of flooding. We have four of five species that are tolerant of flooding but require full sunlight to grow. Those species do very well on newly deposited sand or sediment.”
The majority of the forest, according to Meier, has an existing forest canopy and American elm and green ash are some of the only species that are capable of tolerating flooding but can also survive in shade. These are also the two most common species regenerating in the understories. Elm trees are important for many reasons, including the soft seeds they produce that provide food for wildlife like migratory birds and squirrels.
“We lost most of the American elms 50 years ago and now with green ash trees being eliminated by the emerald ash borer, we basically have a canopy with no regeneration occurring underneath it,” Meier said. “As the forest is dying, it’s a pre-cursor to the loss of forest overall and the conversion of that forest to another cover type.” When the forest converts to another cover type, there are more invasive species such as reed canary grass.
“Our hope is that we'll be able to reinsert American elm back into that process where it will regenerate underneath those existing canopy and stop floodplain forest loss,” he said.
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| Date Taken: | 07.05.2023 |
| Date Posted: | 07.05.2023 14:16 |
| Story ID: | 448572 |
| Location: | ST. PAUL, MINNESOTA, US |
| Web Views: | 139 |
| Downloads: | 0 |
This work, Partnerships promote growth along the Mississippi River, by Melanie Peterson, identified by DVIDS, must comply with the restrictions shown on https://www.dvidshub.net/about/copyright.
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