Penn State geneticists work to save ash trees


UNIVERSITY PARK, Pa. — When Kim Steiner created an ash plantation on the edge of Penn State’s University Park campus in 1978, few Americans thought about “climate change,” no one had heard of the emerald ash borer, and the Yankees beat the Dodgers in the World Series, swinging primarily bats made from ash.

For ash trees, those surely were the good old days.

Garden test

The professor of forest biology in the College of Agricultural Sciences, who is now also director of The Arboretum at Penn State, had 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.

Steiner was conducting a provenance trial, also called a common-garden test — basically moving trees that had evolved in different climates to one location and carefully monitoring their growth and other characteristics.

The goal was to understand how species adapt to their environments.

Fortunately, in the last few decades, the plantation was maintained because of the opportunity it provided to study the effects of climate change on trees.

Collecting seeds

“I knew that I couldn’t get everything I wanted when I sent out two graduate students with funding on a two-week swing through the Midwest and South to collect seeds in wild populations of green ash,” he said.

“So I also mailed hundreds of letters to federal and state forestry employees, park supervisors, fellow scientists — anyone I could get a name and address for — asking for help in collecting ash seeds from local wild populations.”

It turns out that the little-known ash plantation off of Porter Road near the University’s Swine Research Facility — the largest collection of green ash germplasm in one location in the world — likely will play a significant role in saving the species, which is being decimated by an insect from Asia.

Ash borer

The emerald ash borer — often referred to as EAB – is a half-inch long, metallic green, wood-boring invasive that feeds exclusively on ash trees.

EAB larvae feed under the trees’ bark, and they eventually girdle and kill trees within four years of infestation.

They first were identified in North America in Michigan in 2002 and showed up in Pennsylvania in 2007.

They have killed tens of millions of ash trees across North America, and their devastation is so complete that forest scientists worry they will essentially wipe out our native ash species, all of which appear to be susceptible.

Dead ash

Highways through much of the mid-Atlantic and Midwest regions are now lined with the skeletons of dead ash trees.

In Penn State’s ash plantation, in forests across Pennsylvania and in a growing portion of the East, the emerald ash borer is killing nearly all ash trees.

The relatively few that survive or escape — “lingering ash trees,” as scientists are calling them — may hold the key to rescuing the species, and Penn State tree geneticists and other forest scientists are focusing on them.

“As of this fall, 95 percent of the trees in the plantation that were alive before EAB are now dead, and most of the rest will be dead next year. It is amazing how devastating the emerald ash borer is,” Steiner said.

About 15 trees remain after the lastest EAB attack and look pretty healthy, according to Steiner. Holes in the trees bark show the tree was indeed attacked by EAB.


Steiner explained that he is interested in whether some ash populations represented in the plantation are less preferred by the emerald ash borer as indicated by the speed with which they succumbed to the infestation.

Current thinking is that every tree eventually will die under heavy and persistent EAB infestation, but any level of genetic-based resistance could be something to build upon to save the species.

Penn State molecular geneticist John Carlson is looking specifically at the genetic mechanisms by which surviving trees might be battling the insects.

He and Steiner have been talking with officials in the Pennsylvania Department of Conservation and Natural Resources Bureau of Forestry about saving white ash and green ash in the state by preserving and propagating lingering ash trees remaining in the Penn State ash plantation, on state forest lands and in private forests.

“Some trees were left that appeared very healthy with good canopies and not very many EAB exit holes,” Carlson said.

These trees represent potentially resistant genotypes and indicate a genetic tolerance in the trees.

“There have been previous molecular studies comparing lingering versus fully susceptible green ash trees treated with EAB larvae,” said Carlson.


He noted that Jennifer Koch at the U.S. Forest Service Laboratory in Delaware, Ohio, has collected cuttings from many lingering trees after infestations and has developed a bioassay in which the cuttings are inoculated with eggs from EAB, and the growth of the larvae is assessed.

Some of the tolerant trees slow or reduce growth of the larvae; some actually seem to kill the larvae.

Material from all the ashes in the plantation has been collected and is being tested in Carlson’s lab in search of a basis for genetic resistance, and the genomes of those trees that are left are being sequenced.

The genomes of very susceptible trees also are being sequenced so they can be compared to see differences at the genome level that show resistance or potentially tolerant trees.

More research

Determining whether lingering trees are resistant to new infestations will take years.

Steiner and Carlson have offered Penn State’s help to the Pennsylvania Bureau of Forestry and the U.S. Forest Service in setting up at least one grafted seed orchard that contains material from lingering ash trees that have survived EAB infestations.

Then as time goes on, Penn State would assist in evaluating those trees for their level of resistance and develop a seed orchard of resistant trees.

Carlson and Steiner hope to partner with state to create a seed orchard to develop resistant varieties of ash and other trees.

New pests and disease will continue to be introduced and field specialists are needed to find trees resisting disease and other stresses explained Carlson.

As for the future of ash baseball bats, the plight of one iconic brand illustrates ash’s predicament.

For more than 100 years, Louisville Slugger, the official bat of Major League Baseball, has sourced its white ash from a relatively small area of northern Pennsylvania and New York.

Now the emerald ash borer is invading the company’s harvest site.

Steiner visited the Louisville Slugger factory, noting the company is still making ash bats but that will not last long.

“The resource is rapidly disappearing,” he said.


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  1. I hope that thousands of seeds from trees are saved, so that when, not if, but when a solution is found we will have seeds to plant thousands of Ash Trees. Think and act positive.


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