For Richer or Borer: Does Loving Ash Trees Mean Cutting Them Down?
Miss seeing a few of your favorite trees around town? You can shake your fist at a tiny, most unwelcome guest: the emerald ash borer.
This invasive wood boring beetle has killed tens of millions of ash trees in the U.S., and is already on its way to damaging millions more. Unfortunately, removing trees is one common strategy to get rid of the bugger and save the remaining ash forest. To learn more about the problem—and find out why experts say more action is needed—we asked a few expert scientists, arborists, and city foresters for the scoop.
Here Come the Suspects
So, just what is this little bug stirring up all these big problems? The emerald ash borer (EAB), an exotic insect that’s native to China and eastern Asia, hopped a ride stateside in cheap wood packing material more than ten years ago. The adult beetles do little harm, aside from feeding on leaves. It’s the larva stage, however, when EAB chew through the trees and damage their vascular systems (hint: the tissue right under the tree bark that’s responsible for transporting water and nutrients from the roots to the top leaves and branches).
First detected in Michigan in 2002, EAB infestation is now a problem in 19 states, including most recently New Hampshire, where the state’s department of agriculture confirmed detection April 5. Scientists say its continued spread across the country is most likely due to the sale of firewood from quarantined areas across state lines.
Even worse: The stress of climate change, namely drought, makes the trees more vulnerable to EAB, plus North American ash trees have no natural resistance to this foreign guest. In 2012, more than half the continental U.S. suffered from drought so extreme it ranked the 10th largest severe drought since 1895. The recent drought has been particularly prolonged in the Midwest, severely stressing all trees, not just ash.
And the EAB problem is only expected to grow with such a large food source for the pests, arborists explain. Ash trees comprise 10-40 percent of local urban forests, according to one of the nation’s largest tree care companies, The Care of Trees. Many ash trees were planted along streetscapes during the recent housing boom—often together in single-species groups called monocultures that make them easy targets for EAB—and they are natural reproducers.
Lifting the Veil on Some Possible Solutions
So what to do? Initially, many communities responded with a wait and see approach, says Peter Gordon, forester for the City of Lake Forest, Illinois, where 19 percent of the tree inventory is ash. EAB came to attention during the recent economic downturn, Gordon notes, and budget-strained municipalities had few resources to divert to tree treatment.
“The strategy was to see how states, counties, and towns handled EAB where it was first discovered,” he adds. “But now we don’t have as many options.”
Indeed EAB is an epidemic and can’t be ignored, says Fredric Miller, a professor of horticulture at Joliet Junior College and a research associate with the Morton Arboretum in Lisle, Ill. “If you choose not to do any treatment, you will be overrun,” Miller says. “What communities have to come to grips with is that either you are going to manage this on your schedule, or the insect will dictate the schedule.”
And that means, in part, cutting down lots of trees in our neighborhoods in an effort to stop or slow the spread of EAB.
The alternative for a badly infested tree—allowing it to die from EAB damage and then cutting it down—is worse, arborists explain, because it does nothing to prevent the beetle from paying a house visit to the neighboring tree. Plus, Miller points out, dead ash trees are a dangerous liability and must be removed: they’re structurally weak and can fall during wind or ice storms.
But some trees can, and should, be saved with proper insecticide treatment, explains David Horvath, an arborist in suburban Chicago with The Care of Trees. This typically involves injecting the affected tree directly with insecticide; other pesticide treatments involve drenching the soil around the tree with insecticide or lower trunk sprays targeting the bark.
Horvath says that homeowners and municipalities are now charged with identifying “valuable” ash trees—generally larger (greater than 12 inches in diameter)—that provide environmental benefits such as shade to decrease energy demand, a deep root system that mitigates storm water damage, or simply beauty to the property. These are the trees that are considered worth trying to save.
Overall, an integrated approach—treatment, prevention, and some targeted tree removal—is the best way to put the brakes on EAB, and avoid destroying urban forest, say Horvath and the other scientists we consulted.
Prevention and treatment may make more sense economically, too. The estimated cost of treatment, removal, and replacement of EAB in all affected states from 2010 through to 2020 is $12.5 billion, according to a 2011 article in the Journal of Environmental Management. Prevention tactics (such as destroying egg-laying EAB and targeted tree removal) could slash those costs by up to $7.5 billion, the authors concluded.
To put that into perspective, consider the Chicago area, where municipalities spend up to $1,100 to remove and replace one tree, according to a 2012 survey conducted by Miller and his team.
Yes, insecticides may sound nasty, but remember the alternative: cutting down the tree or letting it die anyhow, while giving that nasty beetle a free pass for its next meal. And, when used correctly and responsibly, experts say, insecticides targeting EAB are not likely to harm humans or the environment.
How else are government and science addressing the spread of EAB? Interstate regulation prohibits the sale of firewood from quarantined areas in the U.S. Also any wood packing material used for international trade must be fumigated or heat-treated, explains Kerry Britton, a national pathologist with the U.S. Forest Service in Arlington, Virginia who studies invasive forest pests.
Another strategy: Britton notes that researchers are trying to breed ash trees with natural resistance to EAB by crossing Asian ash trees that fight off the pest with vulnerable North American ash species. “By the time the beetle was detected, it could not be eradicated,” Britton says. “The goal now is to slow it down.”
EcoMyth Outcome: Myth Confirmed
Unfortunately, cutting down infected ash trees is one big part of slowing the spread of the emerald ash borer. The flip side is, those that must fall will help us protect future generations of these beautiful trees.
One Green Thing You Can Do
Follow local rules regarding moving firewood—even pieces of affected bark as small as a credit card can help the buggers spread.
Other ways to help:
- Keep an eye out for EAB, whether in your yard or your neighborhood. Here’s a helpful guide to identifying ash trees and distinguishing between EAB and other problems.
- If you see early evidence of EAB damage in the treetops, your best bet is to call an accredited tree care company. Treating trees by mid-May minimizes the damage by adult beetles, which emerge in the spring. If detected early, trees can be treated with insecticide rather than being cut down.
- Think you spotted one? Report it to your state’s agriculture department office or the call USDA’s EAB toll-free hotline at 1-866-322-4512.