Emerald ash borer creating a crisis in Hennepin County suburbs

Hennepin County's suburbs are seeing a surge in infestations by emerald ash borers, a crisis that foresters predict will wipe out the county's 1 million ash trees within a decade.

Brooklyn Park alone has removed 1,600 ash trees in the past eight years and planted 2,000 trees of different species, barely keeping up with the ones lost. Plymouth has lost several thousand trees this year, even though it wasn't long ago that the city detected its first diseased ash trees in a wooded area.

"The 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's slow moving, the crisis doesn't seem to get the attention it deserves."

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

Foresters found the first ash borer in Hennepin County in the Fort Snelling area. The beetle has progressively moved westward and infested new trees at a rate of a couple of miles annually, DeGroy said.

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

Ash trees were widely planted along boulevards in the 1970s for their beauty. And they're critical in capturing carbon, reducing air pollution, taking up stormwater and providing shade to counteract the urban heat island effect.

The first emerald ash borer was found in Michigan in 2002 and made its way to Minnesota attached to vehicles. Since then, the U.S. Department of Agriculture estimates, the beetle has destroyed hundreds of millions of ash trees nationwide.

Minneapolis has removed every ash tree on public land and replaces about 5,000 trees each year. The St. Paul City Council last year borrowed $18 million to finish cutting down ash trees to replace them with new tree species.

Brooklyn Park didn't have its first ash infection until 2017. About 20% of the city's trees are ash, and 200 of them were removed this year, said Greg Hoag, park and building maintenance manager. Brooklyn Park has received nearly $400,000 from the county and the state to remove and replant ash trees.

Hoag compared the infestation to Dutch elm disease, which destroyed most of the country's American elm trees in the 1970s and 1980s.

"It's really important to take down the dead trees because they become very brittle and dangerous," he said. "The city is getting to the death curve where we are starting to lose hundreds of trees."

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

"You think you are ready to take on this problem, then it explodes," said Plymouth city forester Paul Buck. "It's ramping up in every community, and residents need to have a plan for their trees. Don't wait for the worse case scenario."

Though city officials initially found the ash borer in a small wooded area, it took seven years for it to spread into neighborhoods, Buck said. A good way to identify an infected ash is to watch for woodpeckers peeling off bark, he said.

In the past 1½ years, Plymouth has taken down 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 removed 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 treat the ash before taking them down and others just take them down," he said. "But cities need the budget to take down trees. ... Removing a tree can be hard to do. They all have a story."