Green Digest: Tree wraps explain ash borer threat

Park Board information campaign kicked-off at season's first Open Streets Minneapolis event

Green ribbons tied to ash trees carry information about emerald ash borer. Credit: Dylan Thomas

CARAG — A new campaign to raise awareness about the threat of emerald ash borer debuted during the June 23 Open Streets event on Lyndale Avenue South.

Before the street was opened up that day to bicyclists and pedestrians, the Minneapolis Park and Recreation Board wrapped boulevard ash trees with a green ribbon proclaiming “E.A.B. Kills Ash” and signs that read “Emerald Ash Borer (EAB) is in Minneapolis!” It was fair warning that those trees and thousands of others in Minneapolis faced the inevitable: death by the invasive tree pest or preemptive removal by Park Board forestry crews.

The timing was poignant, with the public information campaign launching less than 36 hours after a powerful thunderstorm downed scores of mature trees across the city. But change is coming to the Minneapolis urban forest, and the Park Board intends to continue the tree wrapping at other events throughout the summer to make sure city residents are prepared.

Ash is one of the top-three most common tree species in Minneapolis on both public and private property, accounting for just over 20 percent of the urban forest, according to Park Board estimates. That includes about 30,000 boulevard trees, many planted after the waves of Dutch elm disease that first hit in the 1970s wiped out most of the majestic American elms lining city streets.

The Park Board response then was to diversify the city’s boulevards, planting whole blocks of ash, maples, disease-resistant elms and other tree species. But the arrival of emerald ash borer a few years ago revealed a weakness of the block-by-block strategy: decades after the ravages of Dutch elm disease, blocks lined with ash now face the possibility of losing all their boulevard trees once again.

The Park Board’s new approach is to plant two or even three tree species on every block, so that the next tree scourge won’t leave behind denuded neighborhoods. In some cases, forestry crews are planting “buddy trees” next to existing ash trees so that a replacement is already in place when the chainsaw comes.

There are insecticides available to protect ash trees from infestation, but the Park Board has no intention of a widespread campaign to save the ash. Emerald ash borers have killed tens of millions of trees in the past decade, and the decline of the ash tree locally is seen as inevitable.

Homeowners can opt to contact a city-licensed tree care company to save a boulevard ash, but they are responsible for the cost. In 2011, Lake Harriet’s beloved “elf tree” — an ash — got a protective chemical injection paid for by People for the Parks, a nonprofit.

The emerald ash borer is native to Asia and was first found in North America in 2002. It already had killed tens of millions of trees in the U.S. and Canada by 2009, when the Minnesota Department of Agriculture confirmed the state’s first known infestation in St. Paul.

In March 2010, a stand of infested trees was identified in Tower Hill Park in the Prospect Park neighborhood, the first confirmed sighting of emerald ash borer in Minneapolis. The discovery of infested ash trees in Lakewood Cemetery this winter marked its arrival in Southwest.

The Park Board’s current goal is to remove no more than 20 percent of the tree canopy on any individual block in one year. City foresters are culling what the Park Board terms “defective and declining” ash now, but will soon move on to removing otherwise healthy small and large ash trees and replacing them with other tree species.

Minneapolis residents can sign up on the Park Board website to have a boulevard ash tree cut down and replaced. To request replacement, or for more information on emerald ash borer and the Park Board’s response, go to minneapolisparks.org/eab.

Nominate a Watershed Hero

Minnehaha Creek Watershed District is seeking nominations for its 2013 Watershed Heroes Awards honoring locals doing their part to maintain clean water in area lakes and streams.

The awards recognize individuals, businesses, organizations and even local governments working to protect the environment and natural resources in the watershed district. The seven award categories are: excellence in development, innovation in government, outstanding partner, youth naturalist, citizen engagement, outstanding contribution and lifetime stewardship.

Nominations are due by July 26 and can be submitted online at minnehahacreek.org/nominate or by emailing watershed district Communications Director Telly Mamayek at tmamayek@minnehahacreek.org. Submissions should include the name of the individual or organization being nominated and a brief description of 200 words or less describing why the nominee is deserving of the award.

The Watershed Heroes Awards ceremony is scheduled for Oct. 17 at the Bayview Event Center in Excelsior.