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A preliminary assessment of potential distributions for Armillaria solidipes and Pseudotsuga menziesii under changing climate within the western USA

Ned Klopfenstein: Rocky Mountain Research Station, USDA Forest Service

<div><span>Armillaria root disease (caused by <em>Armillaria solidipes</em>) causes major mortality and growth loss of Douglas-fir (<em>Pseudotsuga menziesii</em>) in the western USA. How will a changing climate influence Armillaria root disease of Douglas-fir in the western USA? To examine this question, climate-based, species-distribution models using Maximum Entropy were used to predict suitable climate space (potential distribution) in the western USA for <em>A</em>. <em>solidipes</em> and its Douglas-fir host, using bioclimatic variables for contemporary climate and a projected future climate. The projected future climate was based on a representative concentration pathway 8.5, which represents a “business-as-usual” continued rise in greenhouse gas scenario and the global circulation model HadGEM2-ES. With these climate scenarios, results predict that suitable climate for <em>A. solidipes</em> and Douglas-fir are highly correlated, with the predicted suitable climate space moving dramatically northward and to higher elevations. These models indicate that this Armillaria root disease will continue to spread to new climatically suitable locations where both pathogen and host co-occur. We further hypothesize that Douglas-fir will have a higher likelihood of susceptibility to <em>A</em>. <em>solidipes </em>as it becomes maladapted due to changing climate. This interaction could accelerate Douglas-fir mortality on sites where it is maladapted, which could lead to a buildup of woody fuels that contribute to higher fire severity.</span></div>