White ash trees (Fraxinus americana) originally from drier, colder areas are more susceptible to emerald ash borer (Agrilus planipennis) in an arid common garden

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Timber E. Burnette, Division of Biological Sciences, University of Montana, Missoula, MT, Timber E. Burnette, Laurel J. Haavik, James M. Fischer, Jacob Carter, Kistie B. Brunsell and Joy K. Ward, Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS, Laurel J. Haavik, Forest Health Protection, USDA Forest Service, Missola, MT, Justin G. A. Whitehill, Department of Forestry & Environmental Resources, North Carolina State University, Raleigh, NC, Justin G. A. Whitehill, Lina Madilao and Joerg A. Bohlmann, Michael Smith Laboratories, University of British Columbia, Vancouver, BC, Canada, Vaughn A. Salisbury, Kansas Biological Survey, University of Kansas, Lawrence, KS, James M. Fischer, University of Illinois at Urbana-Champaign, IL, Jacob Carter, Center for Science and Democracy, Union of Concernced Scientists, Washington, DC, Joerg A. Bohlmann, Department of Botany, University of British Columbia, Vancouver, BC, Canada, Joerg A. Bohlmann, Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, BC, Canada, Joy K. Ward, College of Arts and Sciences, Case Western Reserve University, Cleveland, OH

Background/Question/Methods: The cascading effects of accelerated climate change are increasing the numbers of insect outbreaks and the frequency of drought in forest settings. These conditions are causing trees to die prematurely across the globe at alarming rates. Tree responses to these challenges can vary due to genetic differences among families (i.e., intraspecific variation). However, it is hard to predict how naïve tree host species will respond to insect attacks from invasive pests. The invasion of North America by emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), a wood-boring beetle indigenous to Asia, has caused widespread mortality of ash trees (Fraxinus spp., Oleaceae), resulting in devastating ecological and economic impacts. To evaluate the intersection of climate with the devastating effects of EAB infestation, we examined intraspecific variation in response to EAB of 44 families of white ash (Fraxinus americana) collected throughout the species range and planted in an arid common garden in northeastern Kansas. We measured tree canopy dieback (leaf loss), drought stress via carbon isotopes, bark healing rates, and chemical defense responses soon after an EAB outbreak at our site.
Results/Conclusions: We found that white ash families originally from drier, colder areas (northern USA) exhibited increased levels of canopy dieback compared to families from wetter, warmer regions (southern USA). Additionally, tree families with more enriched carbon isotopic values and/or slow bark healing rates were more likely to show canopy dieback. Finally, we examined mortality by family and environmental characteristics of seed sources: Only eight families showed significant mortality (defined as 48% or less individuals alive). Of those eight families, four were sourced from the northern USA, one from the mid-Atlantic region, and three from the southern USA. Overall, we demonstrate significant intraspecific variation in white ash canopy dieback and mortality due to emerald ash borer. These findings were strongly connected to temperature, and, to a lesser extent, precipitation conditions of the seed sources.