Posted: March 2, 2020

Research shows some ash trees are resistant to invasive beetles.

"Lingering ash." That's what the U.S. Forest Service calls the relatively few green and white ash trees that survive the emerald ash borer onslaught. Those trees do not survive by accident, and that may save the species, according to researchers in the college who conducted a six-year study of ash decline and mortality.

The research shows that some ash trees have varying degrees of resistance to the strangely beautiful, invasive beetle from Asia.

"We found that genetic variation exists in trees from around the country, and through time--especially as the emerald ash borer population collapses because host trees are rapidly disappearing--the resistance that we observed will likely ensure survival of the species," said Kim Steiner, professor of forest biology.

Steiner, director of The Arboretum at Penn State, collected seeds from wild green ash trees in 27 states and Canadian provinces in the fall of 1975. He grew the seedlings before planting 2,100 of them in a seven-acre plot. Mixed in were a small number of white ash trees.

"We began measuring the decline in 2012, shortly after emerald ash borers arrived in the plantation, and we measured it every year through 2017," said Steiner. The effect of the insect was devastating. As of late 2019, just a few trees remained.

Genetics moderated the rapidity with which the beetles killed trees, said Steiner. "This suggests that some ash genotypes will survive with lower densities of emerald ash borers on the landscape."

--Jeff Mulhollem