Tying green ribbons on the old ash tree

Green ribbons are turning up on ash trees in Minneapolis, a stark reminder of just how much of the public urban forest is about to be cleared away, either by city foresters or the emerald ash borer.

Between the two, nearly all of the 40,000 ash trees on boulevards and in parks will be removed over the next five to 10 years and replaced by other species, said Ralph Sievert, director of forestry for the Minneapolis Park and Recreation Board, which is behind the campaign.

A ribbon doesn't indicate a tree is about to be cut down immediately. Individually, each ribbon provides directions to a park board website about the city's ash borer strategy. But in some parts of the city, nearly every tree on a block — or along several blocks — might get a ribbon, vividly illustrating the potential threat posed by the pest.

Sievert said the public information campaign is designed to raise awareness and explain the city's ash borer strategy, or at least provoke this response: "All these are ash? Holy cow!" he said.

The ribbons are going up in high-visibility areas of the city, often in conjunction with large community events. About 1,000 trees could have ribbons by the end of summer, Sievert said. Several blocks of Lyndale Avenue S. had them in place in June for an Open Streets event. On Tuesday night, residents of the St. Anthony West neighborhood in northeast Minneapolis, where 40 percent of the boulevard trees are ash, put ribbons on trees along Main Street NE. in advance of a community barbecue scheduled for Thursday evening.

"I'm hoping people can be proactive," said Michael Rainville, board member of the St. Anthony West Neighborhood Organization, who lived in the neighborhood a generation ago when the elm bark beetle wiped out its majestic canopy of American elms. "Every one of those trees is going to get diseased and die. We have to work together as a ­community to manage the replacement of those trees."

Some cities and public agencies, including St. Paul, are treating some trees with insecticide to buy some time against the ash borer and prevent a massive tree die-off, as has happened in other U.S. and Canadian cities. Milwaukee is treating nearly all of its 28,000 ash trees with insecticide at a cost of $950,000 per year, indefinitely, said David Sivyer, forestry services manager for the city.

Sievert said that although the insecticide, emamectin benzoate, has been shown to be effective, there has been strong community resistance to the use of insecticides in Minneapolis. The result: a program of steady removal and replacement of all ash trees. Sievert said the city will not take more than 20 percent of the trees off any block in any year.

Minneapolis residents or groups can pay to have public trees treated with insecticide. But even trees treated with insecticide will die of other causes in the coming years, so neither selective removal nor insecticides are likely to prevent the eradication of ash across Minnesota and North America in the next few years, said Seve Katovich, forest entomologist for the U.S. Forest Service in St. Paul. The threat is "dire" to the nearly 1 billion ash trees across Minnesota, he said.

"It's a no-win situation," he said.

The ash borer has killed tens of millions of trees in 20 states and two Canadian provinces while spreading steadily outward from where it is believed to have made its U.S. landfall in the early 1990s — in packing material in a Detroit shipping area. A native of China, the beetle has had no natural predators in North America. Its first Minnesota detection was in St. Paul in 2009.

Bill McAuliffe • 612-673-7646