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Emerald ash borer creates crisis in suburban Hennepin County


Suburban Hennepin County is experiencing an upsurge in emerald ash borer infestations, a crisis that foresters say will wipe out the county’s one million ash trees within a decade.

Brooklyn Park alone has cut down 1,600 ash trees in the past eight years and planted 2,000 trees of different species, barely equal to those lost. Plymouth has lost several thousand trees this year, even though the city not too long ago detected its first diseased ash trees in a wooded area.

“The emerald ash borer has been an ongoing crisis for about a decade, but it’s definitely getting worse,” said Shane DeGroy, a county forester who oversees the tree grant program. “Because it is slow moving, the crisis does not seem to be getting the attention it deserves.”

In response, Hennepin County recently awarded nearly $400,000 to 20 cities, organizations and affordable housing to remove and replace more than 435 ash trees. Foresters say it usually takes two years for emerald ash borers to destroy a tree.

Foresters found the first emerald ash borer in Hennepin County in the Fort Snelling area. The beetle gradually moved west and infested new trees at the rate of a few miles per year, DeGroy said.

According to DeGroy, Minnesota is home to the most ash trees in the country. Hennepin County has about 1 million, and most residents live within 15 miles of an infested ash tree.

Ash trees were widely planted along boulevards in the 1970s for their beauty. And they are essential for capturing carbon, reducing air pollution, absorbing stormwater and providing shade to counter the urban heat island effect.

The first emerald ash borer was found in Michigan in 2002 and traveled to Minnesota attached to vehicles. Since then, according to estimates by the US Department of Agriculture, the beetle has destroyed hundreds of millions of ash trees nationwide.

Minneapolis has removed all ash trees on public lands and is replacing about 5,000 trees each year. Last year, the St. Paul City Council borrowed $18 million to complete the felling of ash trees to replace them with new tree species.

Brooklyn Park didn’t see its first ash infection until 2017. About 20% of the city’s trees are ash trees, and 200 of them have been felled this year, said Greg Hoag, head of maintenance of parks and buildings. Brooklyn Park received nearly $400,000 from the county and state to remove and replant ash trees.

Hoag likened the infestation to Dutch elm disease, which wiped out most of the country’s American elm trees in the 1970s and 1980s.

“It’s really important to cut down dead trees because they become very brittle and dangerous,” he said. “The city is coming to the death curve where we start losing hundreds of trees.”

Plymouth officials had just developed a program to tackle the emerald ash borer problem when the city discovered its first beetle in 2015.

“You think you’re ready for this problem and then it blows up,” said Plymouth town forester Paul Buck. “It’s escalating in all communities and residents need to have a plan for their trees. Don’t wait for the worst case scenario.”

Although city officials initially found the emerald ash borer in a small wooded area, it took seven years for it to spread through neighborhoods, Buck said. A good way to identify an infected ash tree is to watch for spikes sticking out of the bark, he said.

Over the past 1½ years, Plymouth has felled 1,500 ash trees on private property near the Minnetonka border. That’s a significant jump from just two years ago, when 800 trees were felled on private and public land, he said.

A 20-inch tree costs $1,000 to remove, so the cost can add up quickly, Buck said.

“Some cities process the ashes before they take them down and some just take them down,” he said. “But cities need a budget to cut down trees. … Cutting down a tree can be hard to do. They all have a story.”

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