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I was sad to see the mature trees in front of Iowa Chop House (Washington Street) cut down. How come??? — Mary, Iowa City, via email
Those trees were ash trees, and ash trees in Iowa City have been under assault by an insect, the emerald ash borer (EAB), since 2014.
“[The trees] were heavily infested with emerald ash borer, and had many dead branches, which becomes a public health, safety and welfare issue,” Iowa City Director of Parks and Forestry Zac Hall told Little Village last year. “The way ash trees are structured, when they do die or are badly compromised, their branches become very brittle and they become hazards.”
The EAB is from Asia, where ash trees have evolved defenses against the insect that North American ash trees lack. Accidentally introduced into the United States in 2002, the insects were first discovered in Iowa in 2010. By 2014, when the first EAB-infested tree was identified in Iowa City, the city had had a plan in place for nearly a decade.
The Iowa City Parks and Recreation Department stopped planting ash trees in 2004. It also decided to remove any trees compromised by EAB. (The city is only responsible for trees on public land, such as right-of-ways. Property owners are responsible for trees on private property.)
In 2004, that was not a controversial decision. Chemical treatments to combat EAB were generally considered ineffective, and the insecticide used could spread beyond the treated tree and contaminate the soil. But by 2018, things had changed.
Chemical treatments had improved. Coralville, Cedar Rapids and other cities in Iowa opted to treat trees in early stages of EAB infestation, and only removed badly compromised trees.
Residents in Iowa City had also become increasingly concerned about the number of ash trees being removed. There are approximately 3,500 ash trees on public property in Iowa City, making it the city’s second-most common tree — only maple trees are more common than ash trees. But ash trees also accounted for a large percentage of the diseased or damaged trees the city removes each year.
In 2015, the city removed 223 trees, 34 of which were ash trees. By 2017, the EAB infestation had spread, and ash trees were 107 of the 297 trees the city removed.
Ash trees are also more heavily concentrated in older residential areas of the city. Ironically, this is because in the mid-20th century they were considered a good replacement for elms, which were decimated by Dutch Elm disease.
An email to the Iowa City Council from Susan Shullaw, who lives on the Northside, summed up a lot of the concerns residents were having in 2018.
Older neighborhoods such as mine have hundreds of ash trees in the public right of way. If all those trees succumb to EAB, the loss of this mature tree canopy will be felt for decades to come. The disappearance of these trees doesn’t just alter the green and leafy aesthetics of our neighborhoods. Loss of shade trees affects property values, drives up cooling costs, and increases the amount of carbon dioxide released into the atmosphere, exacerbating the greenhouse effect — an outcome that seems to directly contradict the intent of Iowa City’s new Climate Action Plan.
Responding to these concerns, councilmember John Thomas, a retired landscape architect, put a review of the city’s EAB strategy on the agenda for the city council’s Sept. 5 work session.
During the work session, Iowa City Parks and Recreation Director Juli Seydell Johnson explained the city’s EAB strategy and recommended continuing it. Although chemical treatments had improved, Seydell Johnson said they still only delayed the inevitable. It was better to spend the city’s money removing EAB-infested trees and replacing them with a greater diversity of species to prevent the city’s tree canopy from being endangered again by a single pest or disease.
But the city council decided that even if treating infested trees only delayed their demise, it was worth it to decrease the chances of streets with a high concentration of ash trees being denuded, and while saplings planted to replace removed trees are still small. The council directed the Parks and Recreation Department to revise its EAB strategy.
Starting in spring 2019, the city will treat certain infested ash trees that aren’t yet compromised to the point of being a danger to public safety. Viable candidates will be between 9 and 35 inches in diameter, because the insecticide circulates most effectively in trees of that size range. It’s estimated treating viable trees will cost approximately $50,000 a year.
The city’s overall strategy for managing its trees still focuses on increasing diversity through new plantings. In 2017, the year the city removed a total of 297 trees, it planted 578.
Are there even any insect larvae left alive after the late-January polar vortex? Well, extreme cold will kill EAB — unless it doesn’t. The little bastards can convert the glucose in their blood to glycerol, which is pretty much the stuff in your car’s antifreeze. That makes them good to 30 below zero. After that, it’s a matter of how long and how intense the cold is. In theory, a minus 30-plus snap can kill up to 90 percent of an EAB population, but that’s only a temporary dent in the population, since a single EAB can lay 100 eggs. And even that may be too much to hope for. John Vance, Davenport’s city arborist, has been checking to see if the polar vortex killed EAB, and so far, he hasn’t found any frozen or dead ones. He doesn’t think the cold lasted long enough.
This article was originally published in Little Village issue 257.