When foresters recently cleared about 20 ash trees from two blocks of 2nd Street NE. in Minneapolis near Nicollet Island, alarmed residents asked what had happened to the city’s plan to remove trees slowly but steadily over the next eight years.
What happened was a discovery of an infestation by the emerald ash borer, said Ralph Sievert, director of forestry for the Minneapolis Park and Recreation Board. That meant crews had to remove an entire cluster of trees known to be housing the ash borer, a clear and present threat to ash trees around it.
That was an exception to the city’s more-methodical plans to remove 5,000 ash trees per year with less-sudden impact and replace them with new trees. In all, the city will take down 40,000 ash trees over eight years. That’s virtually all of the ash trees on public property.
Sievert hopes to convey the fine points of the city’s ash tree removal strategy in a series of six community meetings beginning March 25.
Indeed, late winter is bringing a bit of urgency to the issue. The Minnesota Department of Agriculture is asking for the public’s help in spotting ash borer infestations, which are more easily detectable while trees are still bare.
Researchers will be looking for impacts of this winter’s deep and lingering cold on ash borer populations and their spread. For now, the cold is likely to mean adult ash borers won’t be emerging from under the bark of ash trees until perhaps June, said Mark Abrahamson, an Agriculture Department entomologist and the state’s chief ash borer detective. But at that point, the tiny beetles will be flying high in the trees and difficult to see, despite their vivid metallic green color. A better clue to their presence is damage from woodpeckers that have been feeding on adult larvae since last fall.
Those who might be doing what Abrahamson called “winter scouting” might also look for cracking bark, a less-obvious type of damage caused as ash trees create new tissue to heal damage caused by ash borer larvae crawling just under the bark.
Abrahamson noted that although ash borers were found in Superior, Wis., last year, they have not officially rounded the west end of Lake Superior to start attacking trees in Duluth or surrounding counties in northern Minnesota.
Researchers are in fact monitoring trees along Duluth’s Park Point, using three different detection methods to find the most effective one, Abrahamson said. They’re looking for woodpecker damage, using detection traps, and cutting limbs off some trees and removing bark to look for beetles underneath.
In Minneapolis, Sievert said, the overall ash removal plan — in the absence of a known infestation — calls for taking a maximum of 20 percent of the trees on any block per year, and only ash, and replacing them with other species. Although some cities, notably Milwaukee, are using insecticide treatments to protect trees, Minneapolis is not. Officials have indicated that there has been too much public opposition, although individuals and groups can pay for inoculation of public ash trees.
Sievert said, however, that the Park Board might inoculate some trees in public spaces, such as those on the Park Board’s Heritage Tree list.