The emerald ash borer, an invasive species responsible for widespread loss of ash trees across Europe and North America. Credit: David Cappaert, University of Georgia Center for Invasive Species and Ecosystem Health

By Miranda Johnson

 

No piece of artwork can rival the beautiful simplicity of brilliant, sun-kissed green leaves against a pale blue sky. Especially in the neatly-manicured, uninspired suburbs of the Midwest, elements of well-placed nature make the view out your window worth seeing. As a child, I’d stand in awe of the beautiful trees on my cul-de-sac, not even fully grown, but radiant still, dotting the streets and bringing color and movement to the landscape. Trees serve a number of important ecological functions, but those of us who grew up on the flat plains of the Midwest have an especially intimate relationship with them; we were sheltered by them, we watched them stretch their limbs across the entirety of the sky, and host birdsong in the mornings and playful squirrels in the afternoons.

Over the span of three years, from 2011 to 2014, I watched the trees on my parkway die from the top down, leaves crumbling, leaving gray, stark branches on the crown. I had seen videos of deforestation in the Amazon and other major forests, but this was happening right outside my bedroom window in Aurora, Ill. Shiny green insects, each no bigger than a penny, had burrowed snaking pathways through the thick trunks, decimating the former beauty of the once-green streets. Only one glorious ash tree remained after the fall of the others of its kind, safe behind my yellow brick house, dripping with vibrant red leaves.

Aurora was not the first town to lose its ash trees. No one knows exactly how or when Agrilus planipennis​, the emerald ash borer, first arrived in the United States. The scientific community generally accepts that it made its way from China, a deadly stowaway concealed within wooden packing materials shipped to the States. The first emerald ash borer in the United States was officially declared present in North America by the United States Department of Agriculture in 2002 near Detroit, Mich. Experts believe that the borer was likely present for 12 years before it was first noticed in Michigan, and probably worked its way unnoticed from coastal shipping points to the Midwest, as evidenced by the widespread damage that it inflicted prior to its official identification. In the nearly two decades since, the emerald ash borer has become one of the most destructive invasive species in the United States.

The bright green beetle has decimated tens of millions of ash trees since the turn of the century. The mark that it has left on the landscape of at least 30 states is permanent. It only took two decades for the beetle to infect trees in more than 30 states, as well as numerous territories in Canada. Reaching a maximum size of only 0.33 inches long and 0.063 inches wide, or about a third of the length of a paper clip, adult beetles do little more than nibble on leaves. Their larvae, however, create deep chasms and pathways within the trunk of ash trees, killing from the inside out, and from the top down. The tiny emerald ash borer can take down trees that are 60 feet tall. Ninety percent or more of America’s ash trees are expected to eventually succumb to the emerald ash borer. The tree in my yellow-bricked house’s backyard has so far eluded the destructive larvae.

Smaller than the radius of a nickel, the larval ash borer’s tunnels through trees are enough to topple forests. Credit: Virginia Cooperative Extension

According to my neighbor, who vividly remembers the fateful day in 2014 when the trees were taken, removal seemed to have come out of nowhere. One minute the city tagged a tree, the next it was gone. My neighbor remembers being told by the contractors removing the trees that the wood was to be burned in an effort to mitigate the spread of the ash borer. But this contradicted information put forth by local and federal government. A report from the city of Woodstock, Ill., in 2009 states that when an infested tree is being removed, wood must be chipped to a size smaller than 1 inch. The Illinois Department of Agriculture also lists methods of disposal, noting that chipping ash debris to less than 1 inch in two dimensions will destroy any hidden EAB larvae and is therefore a proven control method … as well as wood-utilization alternatives. Why, then, would the tree removal company admit to disposing of them in a way that would release substantial quantities of localized pollution into the area?

I spoke to Aurora’s Superintendent of Streets to find some clarity, and he shared a completely different story. According to him, Aurora did not burn its trees. “Our trees were chipped up into mulch by the city and a mulch company. … We also did send some of the trunks of the trees to the sawmill to be made into lumber.” In this instance, it’s comforting to hope that all of the removed ash trees were used as either mulch or lumber.

Despite this, other municipalities have records of trees being burned for disposal. Take Hennepin County, Minn., for example, where all diseased material is removed outside of the growing season and is chipped and burned at private facilities in Plymouth and St. Paul. It’s unclear why any county would choose to burn the removed trees. Whether it was a lack of research or a financial decision, it’s difficult to ignore the absurdity of burning thousands of freshly cut trees. No matter what removal method a municipality used to combat the emerald ash borer, it seems that the best thing that cities can offer their residents is a wealth of information as the situation unfolds. Surrounding cities and municipalities have public statements on their websites from the height of the emerald ash borer infestation in the 2000s and 2010s. Aurora’s municipal website, on the other hand, only states that it has implemented a strategic removal and replanting program to mitigate the impact of tree canopy loss due to the emerald ash borer, with no further report to be found. Over the course of the past decade and a half, the city has consistently promised residents of my neighborhood that it would replace the felled trees. Despite this, the parkway on my street remains treeless.

There is certainly an emotional response to deforestation, but recently scientists at the World Agroforestry Center have asked a poignant question: When we lose an ash, what are we losing? Ash trees have a monumental environmental impact. They improve the quality of air and water by absorbing many pollutants, including sulfur dioxide and nitrogen dioxide. Ash trees also provide necessary habitats for wildlife. One ash tree with a trunk diameter of 25 inches intercepts 6,205 gallons of stormwater runoff every year (and) reduces atmospheric carbon by 736 pounds per year. Stormwater runoff is a major concern of deforestation. It contributes to erosion and the movement of pollutants like pesticides and fertilizers into nearby bodies of water. Ashes also have a light and strong wood that, from a manufacturer’s perspective, is ideal for goods like hockey sticks, baseball bats, and canoe paddles. Though ash trees were harvested for these purposes prior to the ash borer outbreak, they were mainly planted in residential areas because they’re inexpensive and hardy under normal circumstances. As with any plant or animal, these trees are integral members of the ecosystem. If they disappear completely, the impact on the surrounding biome will be serious.

The Midwestern deforestation caused by the emerald ash borer has prompted research into methods to alleviate the damage. Ecologists at the University of Notre Dame have devoted incredible time and effort to the study of the potential survival of ash trees in the face of this infestation. An important element of their research is that, contrary to the popular belief that all ash succumbs to the ash borer’s ruthless deforestation, there are factors that can make some ash trees less susceptible to the emerald ash borer. They found that ash trees with rougher bark were more likely to perish from larvae living within them. A monumental discovery such as this provides evidence that the species may be able to survive the infestation in North America. This study provides a baseline for future ecologists to investigate which environmental factors impact the likelihood of an ash succumbing to the emerald ash borer. It also raises the possibility that some asymptomatic ash trees are destroyed unnecessarily, when instead we might help them survive because they do not threaten other trees.

The outlook seems to be even more bleak, since, according to the Aurora Superintendent of Streets, “this will end up being like the Dutch elm trees. Most had to be removed, but we may end up with a few trees that find a way to survive. We had two Dutch elms that I am aware of that made it through and are down to one maybe that is on private property.” The intention of ecologists and arborists is to preserve as many trees as possible, so having some frame of reference for why ash trees might survive the infestation is imperative to avoid total extinction.

Widespread damage caused by the emerald ash borer. Credit: Troy McCormick via Daily News

With such a fragile situation, the question becomes this: Who gets to decide whether these trees live or die? Many cities and municipalities throughout the Midwest and Northeast made the decision long ago to tag and eradicate all ash trees to eliminate the spread of the borer. In Homewood, Ill., it was a rapid decision. After the first infection was detected in the town in November 2007, the village implemented an ash tree removal practice in spring 2008, resulting in 2,582 cut trees by November of that year.

The tree removal was misunderstood as some sort of panacea and has negatively affected ecological research that relies on having large sample sizes of trees to study. Because a large number of ash trees were removed from an area, those surviving represent a relatively small portion of the original ash population and this proportion is difficult to estimate. Researchers from The American Midland Naturalist​ looked at 290 ash trees and found 80 had died as a result of the emerald ash borer, but they make a point of noting that their results should be taken as very conservative estimates since they can’t account for trees that had been rapidly removed before they conducted their study. The extermination of trees that might have survived has clouded the science needed to understand the impacts of both the emerald ash borer and deforestation as individual issues.

Such broad eradication creates a whole new thread of complications. When healthy trees are removed along with the infected ones to mitigate the spread, the population of ash trees in an area is decimated. Thus, the sample size shrinks to a quantity that’s difficult to analyze scientifically. In an ideal situation, ecologists would be able to conduct research on all of the ash trees in an infected area, whether they were healthy or not. Unfortunately, trees are notoriously difficult to study because they take a long time to grow to adulthood; thus mature trees that are destroyed and replaced with new growth cannot be analyzed. Without clear reports detailing which of the removed trees were infected versus healthy, ecologists can’t get a clear sense of what the most affected zones looked like at the peak of infestation.

Biological controls are one way that ecologists can combat invasive species. By intentionally introducing predators into an environment, the population of a non-native or overgrown native species can be reduced. When searching for solutions to an issue like the emerald ash borer, ecologists ideally want to rid an area of the species as naturally as possible. Introducing natural predators is a common strategy, and was utilized in Michigan in 2011 where two species of parasitoid wasps were approved for release. These wasps, the Oobius agrili​ and Tetrastichus planipennisi​, were officially deemed safe for release in the Huron-Manistee National Forests by an environmental assessment that declared they would not be dangerous for humans or other species besides the borer, making them an ideal tool for population control.

Unfortunately, releasing natural predators can take many years to yield results, so numerous ash trees will still fall prey to the borer as the parasitoid wasps slowly build up in numbers. Because of this timeline, we have yet to know whether this approach has been successful. In the meantime, other natural strategies can be attempted to save the trees, such as wound closure and insecticides. Wound closure is ideal for trees that have not yet been severely attacked, as it repairs the damage done by the borer in the bark and phloem, and allows the trees to be repeatedly infected and survive attacks in the future. Local insecticides, on the other hand, have also yielded promising results. They are also preferable to many arborists as they are applied directly onto the infected tree in a small area, so they are unlikely to harm the surrounding ecosystem. The most successful attempts at saving ash trees usually come from a combination of treatment methods. This could include using insecticides alongside the introduction of natural predators, which may enhance the efficacy of natural enemies by reducing overall emerald ash borer densities and focusing woodpeckers and parasitoids on untreated infested trees. Attacking the invasive species from multiple angles in this way increases the likelihood of tree survival. Unfortunately, such attempts to save trees require resources, time, and money, which may prevent some municipalities from taking action.

Another way to encourage the survival of ash trees is to breed them for resistance. Ecologist Jeff Mulhollem of Pennsylvania State University brought a research team to a group of ash trees in 2012 that survived the emerald ash borer’s infestation to discover why there existed this field of “lingering ash,” as he calls it. His work with the U.S. Forest Service has found that some ash trees have certain amounts of genetic resistance to the emerald ash borer. This allows the tree to withstand infection, or at least delay the infection longer than more susceptible varieties. Mulhollem was able to find evidence that genetic variation could be captured in a breeding program to improve resistance to emerald ash borer in ash trees of multiple species. This is a remarkable find because it allows the evidence of genetic factors influencing ash tree survival to be used as a guide to breed resistant trees. The difficulty with working with trees is that it takes many years for them to mature. Because of this, the reintroduction of ash trees that have undergone a breeding program remains a very distant dream, but a worthwhile goal nonetheless.

The emerald ash borer will cause long-term changes to North American ecosystems. In Aurora, the Superintendent of Streets explains that the city is “still removing Ash trees at this time, (and) about 25,000 to 30,000 trees have been removed.” Not only are ash trees disappearing, but the ensuing reduction in shade alters the growing patterns of other native plants, detrimentally impacting the area’s biodiversity. Animals such as woodpeckers, chickadees, herons, fishers, and salamanders all rely on ash trees in North America. Native biodiversity, and trees especially, are vital to our ecosystems, and the only way to begin to restore this natural balance is by planting new trees in place of the removed ash. Cities and municipalities all across North America included replanting in their emerald ash borer mitigation plans, because of the environmental, ecological, and economic loss that comes with widespread tree removal. The city of Aurora also promised to eventually replace the ash trees with a different species. Named a Tree City USA in 2019, the city must replant trees to maintain its status. Residents also had the option to expedite the replanting process … for a fee of $300. My neighbor who paid for the expedited service waited more than a year for the city to follow through on its promise. Others attempted to treat their trees themselves with the options that were available at the time. But due to the novelty of the emerald ash borer in the region, none of those options were particularly effective and my neighbors were unsuccessful.

Now when I return home, I tend to spend some time with the beautiful ash in my backyard, a pillar of grace and perseverance, proof that these trees may have deserved a chance. The parkway remains bare*, save a few crabapples and other species that didn’t face the grim fate of the ash. My family’s mighty backyard ash is a magnificent reminder of what was, what could have been, and what could be. Maybe it has something those other trees didn’t. In any case, this tree stands in radiant, silent testimony that nature is more resilient than we sometimes think.

 

* EDITOR’S NOTE: The City of Aurora finally replaced the parkway tree outside Miranda Johnson’s residence in 2021 — seven years after the ash was removed.

About the Author …

Miranda Johnson graduated in May 2021 with a degree in Earth, Society, and Environmental Sustainability, as well as the Certificate in Environmental Writing and a minor in Business. She is originally from Aurora, Ill., but has since moved to Seattle after graduation. She started working as a STEM Coordinator at the Institute for Systems Biology in September, and she hopes to continue her career in environmental nonprofit work in the future.

This article was written for ESE 360, the introductory course in the Certificate in Environmental Writing, in Spring 2020.

 

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