The emerald ash borer, an invasive species, was first identified in the United States in southeast Michigan in 2002, according to the U.S. Department of Agriculture. Over the years, this wood-boring beetle has spread across the U.S. and Canada, resulting in the destruction of millions of ash trees, marking it as one of the most expensive insect invasions in forest history. Nearly 90% of ash trees that the Asian beetle attacks ultimately perish, putting the species at risk of becoming essentially extinct in North America. To combat this threat, researchers at Penn State are collaborating with the U.S. Forest Service and other organizations to identify and cultivate ash trees that possess genetic resilience against the beetles and to plan for the restoration of ash trees in forests.
Since 2019, scientists at Penn State’s Louis W. Schatz Center for Tree Molecular Genetics have been concentrating on research involving Oregon ash (Fraxinus latifolia). This species is vital in the Pacific Northwest, as it provides essential habitats for wildlife, strengthens streambanks through its robust root system, cools waterways with its shade, and serves as a food source for various birds and insects.
A recent study, released online prior to its publication in Molecular Ecology, revealed significant genetic diversity in Oregon ash across its geographical spread. The trees, ranging from California to British Columbia, exhibit genetic differences that are influenced by their specific locations due to factors such as population structure, connectivity, and adaptation to environmental conditions. Understanding this genetic variation is crucial to creating ash trees that are both resilient to the invasive pests and able to cope with increasing temperatures, which are essential for maintaining the ecological balance where they thrive.
According to the researchers, the required genomic adaptations to meet future climate challenges, referred to as genomic offset, were most significant in the northeastern regions and least so in the southern areas of the ash species’ habitat. This observation indicates that the geographic distribution of genetic diversity is vital for the long-term survival of these trees.
“The emerald ash borer has been spotted in Oregon and British Columbia, and we anticipate high mortality rates among Oregon ash,” explained Jill Hamilton, the senior author of the study, a professor in ecosystem science and management, and the director of the Schatz center. “Our research is focused on measuring and preserving genetic diversity to aid future resistance breeding initiatives. Penn State is at the forefront of global conservation genetics efforts aimed at safeguarding genetic diversity among ash species, which is key to developing effective breeding and reforestation strategies.”
To reach their findings, the research team examined genetic variations from over 1,000 individual Oregon ash trees collected from 61 different populations across their range, extending from California and Washington to British Columbia. The genetic analysis revealed that despite some connectivity between populations, the scattered distribution of Oregon ash trees could limit the species’ evolutionary potential in the long run.
Hamilton emphasized that protecting the overall genetic diversity of these populations is essential for creating breeding programs that yield trees capable of resisting the emerald ash borer and adapting to climate change.
“Utilizing landscape genomics helps us pinpoint the areas and populations of Oregon ash that require the most conservation efforts and can optimize the selection of populations for breeding program expansions,” she remarked. “Faced with the immediate threat from the emerald ash borer, proactive conservation measures are urgently needed. This study marks the inaugural use of genomic data for conservation and restoration efforts regarding Oregon ash.”
Anthony Melton, previously a postdoctoral scholar at Penn State and now a professor of biology at the University of Montevallo in Alabama, led the study.
Other contributors to this research include Trevor Faske from the Southwest Biological Science Center, U.S. Geological Survey in Flagstaff, Arizona; Richard Sniezko from the Dorena Genetic Resource Center, U.S. Forest Service in Cottage Grove, Oregon; Tim Thibault from The Huntington in San Marino, California; Wyatt Williams from the Forest Resources Division of the Oregon Department of Forestry; and Thomas Parchman from the Department of Biology at the University of Nevada, Reno.
This research received support from the U.S. Department of Agriculture National Institute of Food and Agriculture.
