Pittsburgh's ash, oak trees expected to die off

Borer 'unstoppable,' 165,000 ash in peril

Woodpeckers are already very busy, digging emerald ash borer larvae out of the city's ash trees and loving it.

But folks who like to stroll down tree-shaded neighborhood streets, relax in sylvan backyards or hike through the city's forested parks will have a more negative and potentially more dangerous view of the imminent, massive and costly die off of ash and, to a lesser extent, oak, in Pittsburgh's urban forest.

Over the next three to eight years, as the rat-a-tat-tat of the opportunistic woodpeckers echoes through the city's parks and neighborhoods, more than 165,000 ash trees will likely be killed by emerald ash borer infestation, according to city forester David Jahn. Oak wilt fungus will also claim some of the 45,000 oaks in the city.

PG GRAPHIC PG GRAPHIC The tree terminators

Mr. Jahn said the price tag for cutting down the dead and dying ash, treating relatively few in historic or publicly sensitive landscape areas with injections of a pesticide, and planting some replacements, is $70 million.

"Ash is the larger danger concerning tree losses and expenses," Mr. Jahn said. "All the ash trees we have will be killed except those we pro-actively treat by chemical injection."

On public property within the city, ash comprise about 15 percent of the total tree population. Mr. Jahn said even a fully funded pesticide treatment program will be able to save, optimistically, only about 1,000 trees.

The rest will die within three to eight years, he said, "with heavy, visible losses beginning this year."

The perpetrator of those deaths is the emerald ash borer, a native of Asia, that was accidentally shipped into the U.S. in packing crates and first discovered in 2002 near Detroit, Mich. Since then it has chewed its way very quickly through Michigan, Indiana, Illinois, Kentucky and Ohio, killing more than 20 million ash trees.

"The insect is sweeping the entire country," Mr. Jahn said. "It's unstoppable."

The borers feed exclusively on ash trees and can usually kill a tree within three to four years. Signs of infestation, already easily visible on many ash in the city's parks, include D-shaped larvae exit holes, S-shaped larval tracks under the bark, die-back in the crown of the tree, branching on the trunk, splitting and flaking of bark and woodpecker holes.

It first was discovered in Pennsylvania in Butler County in 2007, according to the state Department of Conservation and Natural Resources. Since then it has defied all attempts to contain it, and has spread quickly throughout the western two-thirds of the state. Ash makes up 7 percent of the state's forested area, but in some northern counties it's found at 50 percent or even higher.

"Louisville Slugger is sweating this big time," said Dave Schmit, DCNR forest health specialist for the 15-county southwestern region, referring to the bat maker's use of ash from the state's northern tier counties. "Pittsburgh has already realized this is coming and is acting responsibly to try to deal with it and not be caught flat-footed."

Mr. Schmit said the ash borer is an "able flier" but its quick dispersal through the state's north and east has been aided significantly by the movement of firewood from county to county despite a state ban on the practice.

He said the U. S. Department of Agriculture plans to impose a statewide quarantine on the movement of firewood out of the state in April in an attempt to slow the borer's northward and eastern migration into adjoining states.

"We've got to move past the culture and habit of cutting trees in one area and moving the firewood to hunting camps or fishing camps or cabins or relatives' homes in other parts of the state," he said. "When you do that you're moving the insect or pathogen around."

The high numbers of forest fatalities the borers will cause will not only hurt the aesthetics of the city's parks and neighborhoods, but also create a public safety hazard because ash trees can fall relatively quickly after they die, said Phil Gruszka, director of parks management and maintenance policies for the Pittsburgh Parks Conservancy.

And the death of so many trees, which store and hold back storm water, also could inundate the city's already overburdened sewer system with billions of gallons of water runoff each year, he said. Massive ash die off and the loss of that forest canopy will also open up those areas for takeover by invasive plants and trees.

"This is the first major metropolitan area in the state that will experience a significant loss of its trees," Mr. Gruszka said. "It's happening. Insects are out there now in ash trees, feeding on the canopy, and we will see lots of dead trees this year."

Only 400 city streets have ash, and health and safety assessments are under way on those, said Lisa Ceoffe, an urban forester and city coordinator for TreeVitalize, an urban tree planting program. But in some nearby municipalities, like Mt. Lebanon, she said, big percentages of the street trees are ash, and most will need to be removed.

"We're not going to stop it. The only way to save select ash is to treat them and that means long-term care," Ms. Ceoffe said. "The emerald ash borer does not observe city or municipal boundaries."

Mr. Gruszka said the city is also dealing with oak wilt fungus, a native fungus common throughout the Midwest and in the mid-Appalachian region, that was found last year in the city's parks. In an attempt to control oak wilt, the city, as part of its "adaptive management" program, last summer clear-cut two acres in Frick Park, two acres in Riverview Park and more than three acres in Highland Park, removing symptomatic oaks as well as adjacent oaks that may have been infected by the pathogenic fungus.

Oak wilt has also been found in some East End neighborhoods and three wooded areas of Allegheny County's South Park.

The fungus, Ceratocystis fagacearum, moves from infected to healthy oaks in two ways: via sap beetles that can carry the fungus spores from tree to tree over long distances, and through the root systems of adjacent trees. The fungus disables the water-conducting system in infected trees, usually those in the red oak family.

The cost of cutting infected oak stands in the city's big parks is about $10,000 an acre, plus another $15,000 to stabilize the soil on the mostly steep slopes where they are found.

Mr. Gruszka said the Pittsburgh Shade Tree Commission will take the lead in approaching city council and the region's foundations sometime in mid-April for funding to do the work. It will also seek federal and state funding and try to sell some of the ash and oak for high-end wood product use to mitigate some of the removal costs.

How many of the ash and oak trees can be saved depends on how much money is committed to aggressively cut the dead and dying trees and treat others that are not yet symptomatic, Mr. Gruszka said. Injection of ash insecticide treatments must be done during a short, three-week period beginning in May.

"If we don't get the money, we will manage the demise of the urban forest. We will cut and remove those trees that are safety hazards," said Mr. Gruszka. "If we do get some money we will still manage the demise of the forest but be able to save more of the trees."

First published on March 27, 2011 at 12:00 am