After the Trees Disappear
Ash Forests After Emerald Ash Borers Destroy Them
By MAGGIE KOERTH-BAKERJUNE 30, 2014
A 2011 photograph from Wisconsin shows what damage the larvae of the emerald ash borer are doing to ash trees in the United States. Credit Image by John Ehlke/The West Bend Daily News, via Associated Press
This past winter was the coldest Detroit had experienced in 36 years. Across the upper Midwest, cities shivered, and more than 90 percent of the surface area of the Great Lakes froze solid.
It seemed like ideal weather to kill an unwanted insect. But it did little to stop the emerald ash borer, an invasive Asian beetle that is devastating ash trees from Minnesota to New York.
“We didn’t find a single dead larva,” said Deborah G. McCullough, a professor of entomology and forestry at Michigan State, who led a study of ash trees in Lower Michigan over the winter.
Even before the severe winter, Dr. McCullough and other scientists had come to the glum conclusion that they were going to lose the decade-long battle against the ash borer. Now they are assessing the cascade of consequences for Midwestern and Northeastern forests, both urban and wild.
The effects will go far beyond what you see on a hike or how you feel about the loss of a tree on your property. They will ripple through forest ecosystems, affecting other plants, animals and water supplies.
An adult emerald ash borer. The larvae burrow into trees during the winter, cutting off access to nutrients and water. Credit Image by Minnesota Department of Natural Resources, via Associated Press
Emerald ash borers do their damage as larvae, eating into the bark and burrowing deep into the trunk to insulate themselves against the cold. In the process, they cut off access to the nutrients and water that the tree needs to survive; it is like severing a human’s network of veins and arteries.
After surviving the unusually cold winter, the beetles emerged in spring as adults. Now they are mating and laying eggs, leaving the next generation of larvae to tunnel through the trees’ internal organs. They can kill an ash tree in as little as two years.
Back in 2002, when the borers were first discovered in North America — in Windsor, Ontario — experts thought it might be possible to eradicate them. But after about six months, researchers realized that the insects had been here for years, probably decades, and had already started spreading across the upper Midwest.
Despite a few moments of optimism since, hope has faded quickly.
“Ninety-nine percent of the ashes in North America are probably going to die,” said Andrew M. Liebhold, a research entomologist with the United States Forest Service.
Nobody was really studying the ecology of ash forests until the borers began destroying them. But now scientists are beginning to see what that change might look like.
A 2009 study in the journal Biological Invasions listed 43 native insect species that rely on ash trees for food or breeding. Those insects are the food supply for birds, including woodpeckers.
“You end up with a different ecosystem that different species prefer and where the old ones can’t do as well,” said Kathleen Knight, a research ecologist with the Forest Service.
Invasive insects have been eradicated in the past, but the invasion must be detected early, while it is still localized.
In the summer of 1998, when the Asian long-horned beetle was found in Chicago, people were already on the lookout for the bug, which had previously turned up in New York. Easier to spot than the smaller and less flamboyant emerald ash borer, the long-horned beetle quickly became the focus of an eradication effort that combined insecticides, public awareness and the felling of hundreds of trees in infected neighborhoods.
In 2007, the beetle was officially declared eradicated in Chicago, but it has since been found attacking trees in Massachusetts.
To tackle the emerald ash borers, scientists have experimented with chemical traps that attract the insects and can help spot the leading edge of an invasion into new forests when they can still be stopped.