Pennsylvania has about 300 million ash trees, state officials estimate.
And every one of them may die soon.
Sometime in the next year or two, almost 370,000 ash trees in Allegheny County -- about one of every 10 -- will die because of infestation by the emerald ash borer. It's an invasive Asian beetle accidentally shipped into the United States more than a decade ago, most likely as larvae in wooden pallets and packing crates, said Philip Gruszka, director of parks management and maintenance policies for the Pittsburgh Parks Conservancy.
Hemlocks -- the state tree -- also are at risk because of the hemlock woolly adelgid, another invasive insect species, and elongated hemlock scale, a fungus. Oaks are threatened by oak wilt, a fungus that can kill a tree in weeks.
But it is the ash trees that are facing certain and near total demise. About 57,000 of them can be found in the city's regional parks -- Schenley, Frick, Highland and Riverview -- where several hundred already have been cut down and the chain saw buzz can be heard almost nonstop.
Dead ash are brittle and large falling limbs pose a public safety risk.
"The ash borer has found every ash tree I've seen so far, and thousands of ash are already dead in the city and county," Mr. Gruszka said. "We're cutting trees every day in the parks along paths, trails and playgrounds and roads, anywhere where there's people, just to mitigate the safety issues. One day in Frick we took down 60 trees."
The city's street ash trees also are coming down. Lisa Ceoffe, an urban forester with the city's Public Works Department, said the city had to cut 50 ash along South Pacific Avenue in Friendship last year and will remove more along the city's streets this year.
She said the city eventually will remove all of the remaining 300 street ash as well as those in high traffic areas of city parks.
"The best thing to do is to go in and do what we have to do, and then restore and replant," Ms. Ceoffe said.
Ash borers feed exclusively on ash trees. The borer larvae live underneath the tree bark, cutting off the tree's nutrients and water flow. Signs of infestation include D-shaped larvae exit holes, S-shaped larval tracks under the tree bark, splitting and flaking of bark, and woodpecker activity.
The bug kills more than 99 percent of the trees it bores into, and most trees die within three years of infestation.
The ash borer has no natural predators in the U.S., and although pesticides have proven to be effective, they are costly and provide only a temporary fix.
The tiny, shiny green bug, first discovered in 2002 near Detroit, has munched a broad path eastward through the forests of 15 states, including those in Michigan, Indiana, Illinois, Kentucky and Ohio in the years since. It was first found in Pennsylvania in 2007 in Butler County and since then has been eating its way east, roughly along the route of the turnpike.
Thirty-one of the state's 67 counties have confirmed infestations, with nine of those added last year, including Chester and Berks, just west of Philadelphia. Cambria County became the 31st county with a confirmed infestation this year.
"Louisville Slugger is worried, I guarantee you," said Dave Schmit, a forest health specialist with the state Department of Conservation and Natural Resources, referring to the manufacturer of baseball bats and one of the big commercial users of ash. "We're completely infested here in the southwest part of the state and we keep finding it in new counties."
The ash borer can fly up to 10 miles in a day, but its primary route to new areas is in firewood transported from one area of the state to another, Mr. Schmit said. Pennsylvania banned the transport of firewood to try to limit the spread of the ash borer but lifted the ban in April 2011 as the number of infested counties grew. A federal quarantine on moving firewood into and out of the state remains in effect.
The ash borer hasn't yet been found in the state's northern tier counties, where much of the acreage is forested and the state's best stands of baseball bat-quality ash are found, but it's only a matter of time, said Sven Spichiger, entomology program manager with the state Department of Agriculture, which monitors and tries to mitigate invasive insects.
"If you look at the national map for ash borer, there are already sizeable infestations north of the Pennsylvania border near Jamestown, N.Y., and our best ash reserves are right near there, too. They're knocking on the door and it's only a matter of time," Mr. Spichiger said.
Mr. Gruszka said the huge number of trees killed by the ash borer will change the water quality and volume in urban and state forests. He said one mature ash tree can cause the evaporation of 2,500 gallons of water a year, and the demise of 200 million trees would result in an additional 500 billion gallons of water entering the state's rivers and streams.
Mark Hockley, a Western Pennsylvania Conservancy forester, said the organization has raised $7 million for a tree planting program and has been working with Treevitalize, a public-private partnership to restore tree cover in urban areas, to plant 20,000 new trees. Approximately 17,500 are already in the ground, including 2,000 in the region's parks.
"We're all about selecting the right tree for the right area," he said. "We avoid hemlocks and we don't plant ash."
To try to preserve a genetic remnant of the locally native ash for eventual regrowth, Mr. Gruszka said the Parks Conservancy, working with the city, has selected and treated 158 of the city trees with a pesticide that is injected into the trunk of the trees. Each tree treatment costs $200.
"We're trying to preserve the genetics of some breeding trees," Mr. Gruszka said. "We've selected historically significant trees, or specimens that are important in their landscapes, and trees that are free of defects. We've selected scattered populations in different parks in case a tornado or microburst hits, so we won't lose all of them."
Don Hopey: firstname.lastname@example.org or 412-263-1983. First Published March 30, 2013 4:00 AM