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In Minnesota, Anticipating the Loss of a Million Acres of Ash Forests—and All that they Do—to Emerald Ash Borer

A wood frog sitting within decaying black ash leaves in a wetland forest in northern Minnesota on the Chippewa National Forest. Photo by Melissa Youngquist, University of Minnesota

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A Minute with the Scientist

Brian Palik: If you were going into a black ash wetland in northern Minnesota, what you would notice is, gradually, you're going downhill from wherever you started walking. And eventually, you'd find yourself, say in mid-spring, standing in anywhere from three to 12 inches of water. And you're surrounded by trees that, for the most part, all look the same to you, because what these wetlands are composed of are anywhere from 90 to 95% of the trees will be one species: black ash.

I'm, Brian Palik. I'm Science Leader for Applied Forest Ecology with the USDA Forest Service Northern Research Station in Grand Rapids, Minnesota. I've been working on this issue of E.A.B. [emerald ash borer] and black ash forests for a decade.

We knew it was headed this way most likely — E.A.B. — moving west and north, but had yet to come to Minnesota. And so, you know, there was this general thought, ‘Hey, we ought to be thinking about this, what's going on, what's likely to go on.’ The aha moment was, I got a call from a forester on the nearby Chippewa National Forest, and he called me up and he just said, ‘Brian, we got to get on top of this thing. We know that the insect is most likely coming our way, and yet nobody's really taking an active approach to be proactive about what to do.’ And the motivation for that was, he and I kind of saying, ‘Hey, there's 1.2 million acres of this forest type in northern Minnesota, and there's virtually no other tree species that are established in those forests to take the place of black ash.’ And that was the motivation for this project, was that phone call and he and I talking and saying, ‘You know, we need to think about not how we stop E.A.B. from doing it’s thing, but how we adapt these forests to the future,’ which most likely will involve other tree species than black ash.

This is the largest expanse of ash forest of any species in the U.S., and so it's something that people have been thinking about, but I feel like myself and my colleagues really were able to get a jump on it in terms of how we've approached this.

Black ash is a foundational species in the wetland forests of the northern Great Lakes region affecting nearly all aspects of ecosystem function. A nonnative insect that has killed millions of ash trees in more than 25 states is edging closer to Minnesota’s black ash forests. Scientists have unraveled the complex relationships between black ash and ecosystem functions and how loss of the species from emerald ash borer, and potential replacement by new tree species, will impact these relationships.

Emerald ash borer is approaching Minnesota’s 1 million acres of black ash wetlands. Northern Research Station scientists and collaborators have developed a framework to understand how black ash, a foundational species, affects ecosystem functions, including hydrology and food webs. They have used this framework to determine how loss of black ash to EAB and replacement with new tree species will impact these functions. Their work uses a large-scale manipulation of wetlands on the Chippewa National Forest to simulate death of black ash from EAB and to evaluate replacement tree species. A key finding is that hydrologic function is closely tied to tree cover; loss of black ash without aggressive replacement with other species leads to marsh conditions. Moreover, leaves of black ash decompose faster than other species, readily becoming food for aquatic invertebrates. Conversion to replacement trees or marsh vegetation will alter food webs and the amphibian communities that depend on them. Promising replacement trees include swamp white oak and balsam poplar; these species will maintain hydrologic function but not aquatic food webs based on black ash leaves. These findings are changing the way that black ash wetlands are managed by state and federal agencies and tribes in Minnesota and Wisconsin.