Rows of stumps line streets once covered by a canopy of ash trees in Des Moines, Iowa, March 2015. AP Photo / Charlie Neibergall

The emerald ash borer hitched a ride overseas on wooden shipping crates. Now it’s eating into municipal budgets.

When a tree dies in a forest, it eventually falls to earth, disputably makes a sound, and inevitably decomposes to become fodder for future generations. When a tree dies in a city street, a private yard, or a public park, it becomes a lethal threat to people and property. City governments and property owners end up paying to safely dispose of the trunk, and the benefits that tree provided to its neighborhood are lost.

In American cities from the Atlantic to the Midwest, this loss is all too real—and urgent. Local governments are digging deep into emergency funds to cut down ash trees that are plagued by a little green bug: the emerald ash borer.

The emerald ash borer hails from China, where local ash trees gradually evolved a resistance to the parasitic insect. Their arboreal cousins across the ocean in America never had cause to, until international shipping connected the two continents like never before. It didn’t take long for the ash borer to dig its way into the wooden pallets used to ship goods around the globe. When it disembarked in the United States, it found a refreshingly familiar banquet of North American ash trees awaiting its arrival, and made itself right at home. Since the early 2000s, these creatures have killed tens of millions of ash trees across 25 states.

An adult emerald ash borer. (AP Photo / Minnesota Department of Natural Resources)

Withering in the Midwest

The emerald ash borer was first identified stateside in Detroit back in 2002, but it had likely been chomping on American wood for some time by then. The insects can’t fly very far, but they managed to spread with some help from humans. When people cut down trees for firewood and take them to market somewhere else, it’s easy enough to carry some pests to a new population. Now they have reached half of the states in the U.S.

The borers settle at the top of ash trees and work their way down, eventually laying eggs beneath the bark. The larvae hatch and eat their way under the bark to dine on the tree matter that circulates nutrients up the trunk. Three or four years can pass before their impact is noticeable. In the end, the outcome is always the same, says Wisconsin state forester Paul DeLong.

This map charts the spread—not always linear—from the emerald ash borer epicenter in Detroit. (USDA)

“Emerald ash borer has been so destructive because it kills every tree it gets into,” he says.

It can be hard to grasp just how big this is without seeing a stricken town up close, but here are some big-picture statistics. There are an estimated 8 billion ash trees throughout the United States. In Wisconsin, for instance, rural forests contain about 800 million ash trees. In the state’s urban spaces, ash trees make up about one-fifth of the population. They’re often planted together, lining city streets or shading backyards. When they all die at once, they starkly alter the look of a city block.

“We got so used to the idea of streets being uniform, the same tree species,” DeLong says. “There’s a recognition now to say that’s maybe not a wise strategy if one’s trying to limit the damage that could be done by the introduction of an invasive species.”

As the trees vanish, so do their ample benefits for urban communities. Without tree shade, city dwellers have to pay more for cooling. They lose the air purification that trees provide. And then there’s the stormwater runoff retention, the health benefits, the potential to reduce crime, and habitat for a range of species. As climate change brings higher temperatures and more intense weather events, the stabilizing effects of trees will only appreciate in value.

Chemicals or death

Communities in affected areas can stave off the inevitable death of their ash populations by applying pesticides preemptively. This costs money and has to be repeated every few years to stay effective. As such, most municipalities can’t apply it to all their ash trees, only the most important ones.

A specialist injects an ash tree in Cleveland with insecticides to keep out emerald ash borers, July 2013. (AP Photo / Tony Dejak)

The alternative is waiting for the trees to die. But that doesn’t work either, DeLong says. If the emerald ash borer shows up and kills off all the local ash trees at around the same time, that puts a huge stress on the city to cut down the trunks all at once, before they fall and kill someone or damage property. To avoid that burden on the budget and human resources, cities have begun cutting down trees before they get infected. That at least helps them spread out the costs on their own terms, and start planting other species.

Chicago hired 26 workers to spray pesticides on their 85,000 city-owned ash trees. Naperville, Illinois, decided to spray its ash trees with pesticides at a cost of $35 per tree per year, rather than cut them down and replace them for $625 apiece. Cincinnati has removed 9,000 of 12,000 city-owned ash trees, at a cost of $4.2 million in emergency funds above the normal budget for tree removal, says Andrea Torrice, whose documentary on Cincinnati’s encounter with the ash borer, Trees in Trouble, is airing on PBS stations this month.

“That’s a lot of money for a post-industrial city that’s still struggling with schools and sewers and so forth,” Torrice says.

Long-term, the outlook is bleak for the ash. Cities will have to get used to a world without them, or dedicate annual funding to keep their meds up to date. The government has been stockpiling ash seeds, in case the environment becomes favorable enough to reintroduce them years down the road. They’re also working on genetic research to breed ash that can resist the little green pests. In any case, the window for containment has closed, leaving only the path of adaptation.

It’s personal

Individuals and families have to pay, too, when the dying trees sit on their property. Torrice first discovered the emerald ash borer crisis when a 45-foot tree came crashing down in her backyard in Cincinnati. She learned that it was an ash, it had been chewed apart by a bug from Asia, and it would cost $1,500 to remove. She was lucky—the tree didn’t hurt anyone, and her insurance company covered most of the expense.

Emerald ash borer larvae leave tracks under the bark of the trees they infest. (AP Photo/Mike Groll, File)

Insurance typically doesn’t pay out for cutting trees down before they fall, though. That means people with a few or a few dozen ash trees on their property have to find the cash to remove them before they fall. Sometimes the city even requires it.

Then there’s the visual and emotional cost, which is harder to put a number on. If you remember playing around a big old tree in your yard as a child, and then have to chop it down because of a parasite, what does that do to you? Or if you’re trying to sell your house but buyers aren’t interested in a once-leafy, now bare residential street?

“We get these lovely, cheap electronic goods from Asia and they use the wooden pallets because they’re cheap, and these local communities are paying the cost,” Torrice says.

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