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Research shows some ash trees have varying degrees of resistance to the emerald ash borer.

February 5, 2020

There is hope for the survival of the ash, according to Penn State researchers, who conducted a six-year study of ash decline and mortality.

The research shows some ash trees have varying degrees of resistance to the emerald ash borer. The study took place at a plantation of ash trees planted on Penn State’s University Park campus in the mid-1970s.

“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 the survival of the species,” says Kim Steiner, professor of forest biology, College of Agricultural Sciences.

Steiner, who also is 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 for two years before methodically planting 2,100 of them, all 12 feet apart, in a seven-acre plot. Mixed in were a small number of white ash trees.

Steiner conducted a provenance trial — moving trees that had evolved in different climates to one location and carefully monitoring their growth and other characteristics — with the goal of understanding how species adapt to their environments. Over the last few decades, researchers maintained the plantation to study the effects of climate change on trees. The ash plantation is the largest collection of green ash germplasm in one location in the world and it may play a role in saving the species.

TOP: Researchers began measuring the decline of ash trees in the Penn State plantation in 2012, shortly after emerald ash borers arrived there, and they measured it every year through 2017. BOTTOM: The ash plantation, with nearly all the trees dead and deteriorating, is now being overrun by plant growth, as this recent photo shows.
Photos by Kim Steiner, Penn State and Lake Graboski, Penn State

“We began measuring the decline in 2012, shortly after emerald ash borers arrived in the plantation, and we measured it every year through 2017,” Steiner says. “As of August [2019], only 13 trees remained of the 1,762 that were alive when the emerald ash borer arrived.”

Genetics moderated the rapidity with which emerald ash borers injured and killed trees, says Lake Graboski, Steiner’s assistant.

“For the first time, this study demonstrated that there is genetic variation that could be captured in a breeding program to improve resistance to emerald ash borer in both white ash and green ash species," Steiner says.

There are three kinds of resistance to insects commonly exhibited by trees, Steiner explained, and more research will be needed to determine which ones the ash trees may be deploying. 

Source:Jeff Mulhollem, Penn State