Minneapolis Parks and Recreation Board replacing trees pre-Ash Borer in favor of diversity


Residents might have seen some ash trees along Stinson Parkway marked with a green painted ring, and concluded that they are being removed because of the emerald ash borer.

That’s all correct. However, those ash trees are not actually infested with the borer. The Minneapolis Park and Recreation Board’s (MPRB) forestry division is removing the trees to try various other species of trees in the same locations.

“We’ve marked 15 trees” along Stinson, MPRB’s forestry director Ralph Sievert said. “We’ll get some new ones planted, and get some diversity going.”

He said MPRB has been working with the Stinson Conservancy, a residents group that’s dedicated to preserving the urban forest along Stinson. He said letters were sent to nearby residents, and that they’ve heard “no real objections from the folks living there.”

So, while it might be considered good news that the local infestation hasn’t moved this far north, it’s only a small comfort. Sievert says the demise of most ash trees in the area is inevitable, probably within the next five-to-10 years. “But it could be even sooner than that,” he said.

While they’re pleased that the infestation isn’t growing rapidly now, he said that research in other parts of the country indicate that “there’s kind of a death curve…it’s just a matter of time before [the infestation] finally does take off.”

And, “Every year we’re finding more of them.”

The borer, which is native to China, reproduces under the bark of ash trees and tunnels into the wood, eventually cutting off the flow of water and nutrients from the tree’s roots to its trunk, branches and foliage. It was first detected in the U.S. in 2002 near Detroit, Mich. The only known local infestation is near Highway 280 and Interstate 94, spreading north to about Como Avenue and south and west to the Mississippi River, with a few infested trees found across the river on West River Parkway.

Sievert said that only one infested tree has been found in Northeast, in the 300 block of Second Street NE. “Our folks found that tree while they were doing other stuff,” Sievert said. He said that in a few nearby blocks, all the trees are ash trees, but that no other infested trees were found.

“As we’re planting new trees, we’re really trying to get a lot more diversity,” he said. When the Dutch elm disease epidemic started, he said, 90 percent of the area’s tree cover was elm trees. He said some people have asked if they didn’t learn the diversity lesson from the Dutch elm problem. He said they did learn the lesson, but that at that time, “diversity was block by block.” So they planted many species of trees to replace the elms, but “that’s not much consolation to the person who lives on the ash block.

“Now we’re diversifying in [smaller] groupings,” but it’s a tricky balance, because one tree might not sufficiently show off a given species’ attributes. So “we’re still clustering so we can get the aesthetic effect.”

There is hope for individual ash trees, Sievert said. “There are pesticides you can use to preserve the tree.”

Home owners who have ash trees in their yards can call the Minnesota Department of Agriculture’s Arrest the Pest Hotline at 651-201-6684 for information.

The problem has economic repercussions as well as the more obvious environmental and ecological consequences. Ash trees provide wood for a multi-billion-dollar industry that produces furniture, tool handles and other wood products. The borer can wipe out acres of trees even in a relatively brief infestation.

Common treatment plans have included destroying infested trees, “girdling” infested trees with borer attractants to draw borers to already-infested trees and away from healthy ones, insecticide treatments to save individual trees, and quarantine policies to keep people from transporting potentially infested wood to uninfested areas.

Minnesota researchers are also studying the effect of introducing a species of tiny stingless predatory wasps, also native to China, on the expected infestation growth. The wasps’ only known prey is the emerald ash borer.