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Research Aims to Save Oregon Ash Trees from Invasive Pest

The emerald ash borer, an invasive insect native to Asia, was first detected in the United States in southeast Michigan in 2002. Over the years, this wood-boring beetle has spread across the U.S. and Canada, resulting in the demise of tens of millions of ash trees. This event has triggered one of the most expensive forest insect invasions to date, with over 90% of infested ash trees succumbing to the pest. The situation threatens to render the ash tree species functionally extinct in North America. In light of this crisis, researchers at Penn State University are collaborating with the U.S. Forest Service and various partners to identify ash trees with genetic resistance to the beetle and to devise strategies for restoring ash populations in forests.

Since 2019, the Louis W. Schatz Center for Tree Molecular Genetics at Penn State has concentrated its research on Oregon ash (Fraxinus latifolia). This species plays a vital ecological role in the Pacific Northwest, offering habitat to wildlife, stabilizing streambanks, providing shade to cool waterways, and serving as a food source for various birds and insects.

A study recently published in Molecular Ecology highlighted significant genomic variation within Oregon ash across its geographical range. Researchers discovered that the genetic characteristics of these trees, which stretch from California to British Columbia, differ based on their specific locations. This variation is shaped by factors such as demographic influences, the connectivity of the range, and adaptive responses to environmental conditions. Identifying this genetic diversity could be crucial in developing stronger ash trees that can withstand the pressures from both the emerald ash borer and increasing temperatures, as the researchers noted that no other tree species fulfills the ecological role of the ash in this area.

According to the study, the estimated genomic changes necessary for Oregon ash to adapt to future climate conditions, referred to as genomic offset, showed the greatest need in the northeastern parts of the species’ range and the least in the southern areas. These insights suggest that understanding the regional distribution of genomic variation is essential for the species’ long-term survival.

“With the recent sightings of the emerald ash borer in Oregon and British Columbia, we anticipate similar mortality rates in Oregon ash as we have observed elsewhere,” stated Jill Hamilton, senior author of the study and associate professor in ecosystem science and management at Penn State. “Our efforts focus on quantifying and preserving genetic diversity, which is vital for future resistance breeding initiatives. Penn State is at the forefront of international conservation genetics to maintain this diversity across ash species crucial for reforestation and breeding programs.”

The researchers evaluated genomic variations from over 1,000 individual Oregon ash trees collected from 61 distinct populations spanning California, Oregon, Washington, and into British Columbia. Their analysis showed that while there appears to be connectivity among these populations, the fragmented distribution could hinder the species’ evolutionary adaptability over time.

For breeding programs aimed at developing resilient, emerald ash borer-resistant trees, it will be imperative to preserve the genomic diversity present across the species’ range, Hamilton emphasized.

“Utilizing landscape genomics allows us to pinpoint regions and specific Oregon ash populations that require conservation efforts most and enhances our ability to select populations for breeding programs,” she noted. “Given the pressing threat of the emerald ash borer, proactive conservation measures are essential. This study marks a pioneering application of genomic data in the conservation and restoration strategies for Oregon ash.”

Anthony Melton, a postdoctoral scholar at Penn State, led the study and is now a professor of biology at the University of Montevallo in Alabama. The research team included experts from various institutions, including Trevor Faske from the U.S. Geological Survey, Richard Sniezko of the U.S. Forest Service, Tim Thibault from The Huntington, Wyatt Williams from the Oregon Department of Forestry, and Thomas Parchman from the University of Nevada, Reno. The work received support from the U.S. Department of Agriculture National Institute of Food and Agriculture.

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