Marching across much of the U.S., beetle poses a threat to campus trees

Devin Livi, associate director of grounds and landscaping, with sections of the trunks and branches of two historic ash trees removed from Cannon Green last summer.
Ricardo Barros

Some of the oldest and most historic Princeton trees are ash, including the Lafayette Ash on Front Campus, dating from the 1820s. But as the campus braces for the onslaught of the emerald ash borer, an invasive species of Asian beetle that kills 99 percent of afflicted ash trees, a pair of magnificent specimens planted on Cannon Green in about 1836 have been taken down because they were deemed too frail to try to save.

A metallic green beetle, the emerald ash borer has done extraordinary damage in the United States since arriving from China, probably in a wooden palette used for shipping. It appeared in Michigan 14 years ago and has spread to more than half the states. The crisis has been compared to the chestnut blight of a century ago, which eradicated an entire species from forests and parks, with billions of trees dying.

Having made a long march eastward, the dreaded emerald ash borer showed up in New Jersey in 2014, and one was discovered near Princeton Stadium in August. Their larvae burrow beneath the bark of ash trees, cutting off the flow of nutrients, and so the tree quickly dies.

Emerald ash borer
Minnesota Department of Natural Resources via AP Images
Ash trees abound at Princeton, their rich fall color having long made them a favorite species for planting in American parks. The University has identified three classes of ash tree on campus: heritage trees of great age and historical interest, young trees, and middle-aged trees. “We can’t treat every tree,” said Devin Livi, associate director of grounds and landscaping, and so only the first two categories have been receiving injections and bark sprays against borer infestation. The countless ash trees in the forest near Lake Carnegie, which dates to at least the 1830s, also have not been treated.

“We are being as proactive as we can,” Livi said, but he pointed to the almost total extermination of ash trees in the Midwest: “Nothing has been effective, as far as I can see. I think you’ve got only a 50-50 shot on the ones that we are treating.”

Two of the three enormous ash trees on Cannon Green (see “Our Unforgettable Trees,” PAW, May 14, 2014), measuring 12 and 15 feet in girth, were cut down in August. A ring count proves they were planted 180 years ago, and every Princeton student since antebellum days had walked under their shade. But they were weakened by age, and with the emerald ash borer’s arrival, the University thought it prudent to remove them.

Not only the campus will feel the impact of this insect plague: The town of Princeton has 2,000 ash trees along its streets, and is asking residents to “adopt” ash trees by paying for preventive treatments.