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Surviving ash trees may hold key to saving multiple species of the trees

by Jeff Mulhollem, Penn State

UNIVERSITY PARK, Pa. — The invasive insect emerald ash borer is killing ash trees at an unprecedented rate in the United States, and now five North American species of ash are considered critically endangered, according to the U.S. Department of Agriculture (USDA) Forest Service. But a small percentage are surviving, and research by Forest Service scientists suggests that those trees may hold the key for saving the species.

In an effort to unlock the answer, researchers in the Louis W. Schatz Center for Tree Molecular Genetics at Penn State are working with The Nature Conservancy and the USDA Forest Service to conduct genomic analysis of range-wide collections of green ash, white ash and black ash. Led by center director Jill Hamilton, associate professor in ecosystem science and management in the Penn State College of Agricultural Sciences, they will assess range-wide genetic variation that could guide resistance breeding and restoration efforts.

Graduate student researcher Kyra LoPiccolo measures a white ash

as part of a common garden experiment in Lawrence, Kansas. Credit: Penn State. Creative Commons

“We will leverage a combination of ash provenance trials established in 1978 at University Park by Penn State Professor Emeritus Kim Steiner, existing collections available through the USDA’s Germplasm Resources Information database, and new collections by Penn State graduate students and partners to assess genetic variation in these three ash species across their range through time,” she said. “We also are planting thousands of black ash seedlings this spring. Genetic variation will be associated with environmental variation to quantify contemporary genetic-environment associations.”

The devastation has huge implications for both forests and people, Hamilton said. The potential loss of these trees can have impacts on wildlife, local economies, regional culture and the forests’ ability to help fight climate change. The grim prospect has led to partnerships that will hopefully conserve a culturally significant legacy.

Black ash, especially, has ecological and cultural significance, Hamilton explained. It can thrive in boggy environments, such as swamps. Its root system essentially holds together the entire ecosystem. Without black ash trees, the habitat would convert from swamp to open, marshy wetlands.

The Wabanaki people, who have lived in the region now called Maine for some 12,000 years, link the story of their creation to black ash. Today, members of the four Wabanaki nations — the Maliseet, Micmac, Penobscot and Passamaquoddy people — continue to use black ash as the principal building material for baskets, which are used and sold as tribal art. Black ash remains a vital part of Wabanaki cultural identity and the local economy.

This image shows the damage on a dead tree in an ash trial

planted in 1978 at Penn State. Credit: Penn State. Creative Commons

The Schatz Center team at Penn State has partnered with John Daigle, a social scientist and professor of forest recreation management at the University of Maine, to provide expertise on conserving the species genetic variation long term via seed collections and propagated range-wide material that may represent a legacy of forests that no longer exist today. Daigle, who is a member of the Penobscot Indian Nation, studies the emerald ash borer and its impact on trees and Wabanaki tribes across New England.

The collections and genomic resources developed through this project, Hamilton pointed out, will contribute to and expand upon existing ash-breeding programs aimed at developing resistance to the emerald ash borer, in collaboration with USDA Forest Service and The Nature Conservancy, which provided a $200,000 grant to Penn State to support this research.

“The few surviving trees, called ‘lingering’ ash trees, may hold the genetic keys to breeding trees resistant to the damage inflicted by the emerald ash borer,” Hamilton said. “Heritable genetic resistance to the pest will be a key resource needed to cultivate resistant trees for generations to come, which can then grow into future healthy forests.”

However, The Nature Conservancy’s commitment to restoring tree species imperiled by non-native forest pests is about more than ash. The conservancy also funds a region-wide research and outreach program with the goal of developing and accelerating resistance breeding and restoration efforts for five of the currently most critically threatened trees of the Eastern deciduous forest, including the American beech and Eastern hemlock.

A close collaboration with the USDA Forest Service, experts from academia and research organizations, the work is billed as an urgent race to save North America’s iconic trees imperiled by invasive pests and pathogens. Besides Penn State, The Nature Conservancy also has enlisted the universities of Connecticut, Tennessee, Notre Dame, Cornell, and Washington and Jefferson College to collaborate on the effort.


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