13 years after emerald ash borer's arrival, metro Detroit communities embrace tree diversity

Detroiter Kevin Bingham is well acquainted with the plight of southeast Michigan's ash trees. As a tree caregiver, he's been working with various tree services in the metro area since 2001. Bingham noticed an upsurge in clients wanting ash trees pruned in 2002, followed by a spike in removal requests the next year. The "main catastrophe" hit Detroit and its suburbs between 2004 and 2007, when, he says, tree care companies were "removing them left and right." After that, there wasn't much left to do. Nearly all mature ashes in the area had been wiped out.
The source of this scourge is a species of small green iridescent beetle, called the emerald ash borer (EAB). Native to Asia, it was first discovered in the U.S. in 2002 in Canton, Michigan. Once here, the beetles sought out local ash trees and laid eggs in them, spreading further through infested firewood left at campsites.
Bingham has no trouble recalling what happens to trees infested with the insect's larvae.
"Basically the tips of the branches will die, and then in response it will shoot out a bunch of suckers from the middle of the trunk," he says. "You'll also start to see holes on the tree—little D-shaped holes with the ash borer drilling—and they go in there and they just swarm around underneath the bark, cutting off the flow of nutrients to the tree."
This starves the tree, and it's effectively a death sentence.
The big picture consequences of the loss of elms have been dire, particularly in urban areas where trees reduce the urban heat island effects and reduce stormwater runoff, as well as add to property values.
The Michigan Department of Natural Resources (DNR) estimates that millions of ash trees across the state have been wiped out. EAB is now considered established in Michigan's Lower Peninsula, and its spread is being watched in the Upper Peninsula. Currently, the beetles have been detected in 25 states nationwide, as well as in the Canadian provinces of Ontario and Quebec.
A 2014 study by Daniel Herms of Ohio State University and Deborah McCullough of Michigan State University found that in some forests near the southeast Michigan epicenter of the infestation "more than 99 percent of the ash trees with stems greater than 2.5 cm in diameter" had been killed. That said, it's important to note that Southeast Michigan's forests are a blend of different tree species, including sugar maple, basswood, beech, hemlock and more, not just ash.
In urban areas, where ashes had been popular street trees, the devastation has been close to 100 percent. After Dutch elm disease killed off the area's ubiquitous elm trees in the 1950s, many urban planners in Detroit and nearby communities replaced them with ashes. This decision would prove costly.
"Economic losses in terms of street and landscape trees vary widely from community to community and are difficult to quantify," says Roger Mech of the DNR's Forest Resource Division. "Losses to property value, costs of removal and replacement, treatment costs, etc. have been significant."
"Many estimates project losses in the billions of dollars as EAB continues to spread," he adds.
As bad as this sounds, Wayne State professor Dan Kashian, a zoology and forest ecology expert who's been researching the issue for several years, says it could be worse.
Contrary to early doomsday talk, Kashian points out that while EAB has ravaged local ash trees, it hasn't wiped out Michigan's mixed-tree forests. What's more, the ash population appears to be rebounding. Some trees are springing back up out of trunks like bushes, and others are living long enough to sow replacements.
"I'm starting to suspect ash is going to be around," Kashian says. "We're not going to find big beautiful ash trees anymore, but they'll be a lot of small and scrawny ones, because they are able to produce seeds before they are completely wiped out."
Unfortunately, emerald ash borers are sticking around too, though in smaller numbers then a few years ago. To protect remaining trees, communities like the Grosse Pointes have taken to injecting insecticides into individual ash trees to help them stay alive. The process works, but it's expensive and must be repeated. For this reason, the city of Grosse Pointe canceled its treatment program.
Around Lansing and other parts of southeast Michigan, biological control in the form of Chinese parasitoid wasps has also been tried. They kill the beetles by laying eggs inside them. But Kashian says this controversial tactic came too late, since the wasps weren't introduced until after EAB were firmly established in the region.
The professor says the best approach for communities to dealing with invasive situations like EAB is planting a diversity of different trees.
Sal Hansen, the Greening of Detroit's senior community forester, agrees wholeheartedly. In the wake of the ash borer's assault, his organization has been replanting Detroit area streets with 26 different tree species, including green vase zelkova, greenspire linden, gingko and various oaks.
"We're trying to avoid a monoculture," he says. "We really want to have a variety of native and non-native, urban-tolerant, street-appropriate trees."
He feels this is vital in ash-devastated Detroit.
"Trees provide a ton of environmental and health benefits, especially as they get larger," the forester says. 
These include lowering temperatures, absorbing stormwater, lowering air pollution and reducing stress and crime, according Hansen.
For these reasons, he believes it is important for communities to look at planting different trees to make local ecosystems more resilient to threats and to prevent invasive tree species, such as mulberry and ailanthus, from crowding out biodiversity.
As for other potential pests, Michigan's DNR is currently monitoring for the hemlock wooly adelgid, which kills hemlock trees, and the Asian longhorned beetle, a threat to maples that was recently spotted near Cincinnati.
With threats like these looming, it is important to be mindful of the need for tree diversity. If you need a reminder, just look up next time you walk under a shady tree.
This story is a part of a statewide Invasive Species/Forest Management Community Impact Series. Support for this series is provided by the Michigan Department of Natural Resources.
David Sands is a Detroit-based freelance writer. Follow him on Twitter @dsandsdetroit.
All photos by Nick Hagen.
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David Sands is a Detroit-based freelance writer. He's covered the news for Huffington Post Detroit as an assistant editor and worked as a staff writer for the transportation news site Mode Shift. Follow him on Twitter @dsandsdetroit.