As deadly infestation continues to take toll on ash trees, city pursues grant that would help buy replacement species
The mortality of Port Washington’s ash trees, which have been under siege by the emerald ash borer since at least 2012, is beginning to peak, city forester Jon Crain said Tuesday.
“Mortality is exploding right now, especially in natural areas,” Crain said.
That’s especially easy to see in areas such as the Sauk Creek Nature Preserve and the ravine, Mayor Tom Mlada said.
“You can see the impact everywhere,” he said.
To help mitigate the impact, the Common Council on Tuesday approved a resolution seeking a Forest Service grant that could provide as much as $20,000 to replace trees killed by the emerald ash borer.
If the city were to receive the maximum amount, it would be able to purchase about 200 trees to replace dead or dying ash trees, Public Works Director Rob Vanden Noven said. Most would be planted along the streets, but some would also go in the city parks.
The city would provide the required 25% match through the labor needed to plant the trees, he added.
“I anticipate we’ll be planting over 400 new trees next year,” Vanden Noven told the Common Council. That number includes replacements for not just ash trees, but also maple trees that are in decline as well.
Last year, the city cut down almost 250 ash trees that were growing along its streets, Crain said.
“We really focused on getting a lot of the larger ones out last year,” he said.
Of the approximately 1,100 ash trees that once grew along the city streets, about 600 are being treated against the borer, Crain said, and 400 have been cut down.
In addition, roughly 200 ash trees in parks and natural areas have been cut down, he said.
The remaining 200 or so ash trees along the streets that haven’t been treated will die in the next several years, Crain said, as will untold numbers in the natural areas.
The city will take down those in natural areas depending on the risk they pose to pedestrians, he said, while the majority will be allowed to fall naturally.
“There are a lot of areas that are just too dangerous to get to for us to remove them,” Crain said, particularly along the bluffs and ravines. “We’re going to handle them on a per-case basis.”
The emerald ash borer was first discovered in Wisconsin near Riveredge Nature Center in the Town of Saukville in 2008.
The borer, a bullet-shaped insect about one-half inch long and one-eighth inch wide, infests all types of Fraxinus ash trees, including green, white and black ash.
It burrows into the bark and lays its eggs. When the larvae hatch, they chew through the fluid-conducting vessels under the bark, cutting off the flow of water and nutrients to the tree and eventually killing it.
Port Washington was the second location in Ozaukee County to report the borer, and Crain said the damage it’s caused is proceeding along a timeline that’s long been predicted.
“It’s happening right on the timeline we expected,” he said.
Models show that in the first seven years or so after the borer infests trees in a community, mortality is 20% to 30%, Crain said, and in years eight to 11, it’s 80% to 90%.
“That’s what’s happening right now,” he said. The borer was first discovered in Port in 2012, but was likely in the city for several years before that.
The trees that the city has treated are doing well, Crain said.
But the remaining ash trees are dying, he said.
“This year and the next the numbers are going to be huge,” Crain said.
In a couple years, the borer will have destroyed virtually all the untreated trees, at which point the city can evaluate the treatments it is using and perhaps scale back on them, he said. Instead of treating ash trees every two years, the city may be able to stretch that out to three years.
“At that point, the insect is going to run out of its food source. Its numbers are going to go down, and it’s not going to pose as much off a threat,” Crain said. “We’ll see how it’s going.”
Vanden Noven said he’s sure the city will be able to scale back treatments in a couple years, or that the invasion will be on the decline then.
“I’m not quite as optimistic as Jon,” he said.
But, he said, the city’s decision several years ago to treat many of its ash trees was a good one.
“A lot of communities have decided to let their entire ash tree population go,” he said. “To lose that in a year or two would just be devastating.”