Beyond Killing Trees, Emerald Ash Borer May Leave Lasting Impression
The Emerald Ash Borer has all but wiped out ash trees in and around the Pittsburgh region, and even though the insect only goes after one tree species, the effects will be felt on a much wider scale.
Pretty soon you won’t be able to tell dead trees from live trees as leaves begin to fall. For now, as you’re driving around Pennsylvania, you can look out over stands of trees and see lush, green landscape – but – that landscape is dotted in many areas with dead trees.
“When you spot a dead tree, there’s a good chance, 90 percent chance, that it’s an ash tree that’s already been taken by the Emerald Ash Borer,” said Doug Metcalfe, owner and operator of Aerial Arborist Tree Service. “It’s not really an overstatement to call it a plague of biblical proportions, because I see a lot of trees and nearly every Ash tree has some signs of infestation.”
The small insect, native to Asia and Eastern Russia, has been in the U.S. since the early 2000s. It was first confirmed to be in Pennsylvania in 2007. Once a tree is infested it can take the Ash Borers three to four years to kill it.
“It means literally nationwide billions of dollars of cost for tree removals, but beyond that – the environmental cost of potentially losing a species of tree,” Metcalfe said.
That environmental cost is on the minds of many, including Matt Erb, the director of urban forestry at Tree Pittsburgh.
“Because these trees are dying in the middle of forest stands, creating open patches of canopy where sunlight is coming in and hitting the forest floor, and so that opens the forest up to be invaded by invasive species,” said Erb.
And that, he said, can change the makeup or ecology of forests or parks.
“In some of these areas where we’re losing ash (trees), we’re going to start to see more Bittersweet Vine, we’re going to see more Honeysuckle, more Ailanthus,” said Erb, “more of those invasive trees that take advantage of an opening in the tree canopy when they can.”
Plus, trees have numerous environmental benefits, such as pollution reduction and stormwater retention, so the loss of an entire species is concerning.
“Our street tree population of 30,000 trees absorbs 42 million gallons of stormwater per year, so that’s pretty significant,” Erb said. “If we look at our park trees and our hillside trees, we’re talking probably billions of gallons of stormwater per year.”
Taking Down the Dead
Erb estimates ash trees make up about 9 percent of the tree cover in the city. Dead trees have to be taken down around trails, roads or any place there are a lot of people and structures, “but trees that are in the middle of the forest, they do still provide a lot of wildlife habitat to birds, a lot of mammals that nest in trees, so leaving some of those trees is fine.”
Ash trees can be treated with an insecticide, and a few around the city have been and are hanging on, but treatment is costly and time consuming. There are also some young ash trees, and the Emerald Ash Borer prefers older, established trees. But mostly, Erb said, the effects of the insect can’t be undone.
“We’re going to have a lot of work to do to restore the canopy of our urban forest,” he said.
To that end, organizations like TreeVitalize have efforts underway to plant more trees – just not ash trees.
“You’re sort of feeding the pest if you keep planting the same species, so our strategy for planting is diversity,” said TreeVitalize Director Jeffrey Bergman.
TreeVitalize works with organizations and municipalities on replanting efforts. Since 2008, they have planted some 22,000 trees. Not all plantings are related to the Ash Borer, but many are.
“In Ohio Township for example, they lost large areas of forest because they were mostly ash. So the trees they received through our program specifically went to reforest those areas,” Bergman said.
When there are large plantings, several different species are planted together, but as ash trees come down and new trees go up, some areas will take years to fully recover.
“These efforts are pretty new,” Bergman said, “so we actually don’t really know what the long-term efforts are necessarily, so I can’t say, ‘In 25 years, we’ll have blah blah blah…,’ but it’s a long-term effort and we understand that.”
As for the bug itself, the Emerald Ash Borer, it’s in all but about 12 counties in the commonwealth.
“A scary thought to me is once they’ve taken all the ash trees, there’s going to be this huge amount of Emerald Ash Borers and will they evolve? Will they evolve to go after another species – a worst case scenario a Maple or an Oak?” said arborist Doug Metcalfe.
Entemologist Sven Erik Spichiger, with the Pennsylvania Department of Agriculture, has a preliminary answer.
“So far there has been no evidence of that occurring in other areas where Emerald Ash Borer has gone through,” Spichiger said. “I know there have been some laboratory tests that show that it will hit some other trees, but it does not do well there.”
In those tests, the insects go for species that are closely relate to the ash tree, and he cautioned, this isn’t definitive proof.
“It seems like they can attack them, but they don’t do well on them and they don’t survive, but again, this was only in a laboratory and has never been documented in the field,” Spichiger said.