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1. Lalande, Bradley. Abiotic and biotic factors influencing western United States coniferous forests.

Degree: MS(M.S.), Bioagricultural Sciences and Pest Management, 2019, Colorado State University

In the next decade, climate models suggest that global temperatures will continue to rise. In the western United States, increases in temperatures and changes in precipitation patterns will escalate the risk of drought conditions. These potentially warmer, drier conditions could induce physiological changes within trees, subsequently increasing stress on coniferous forests that are adapted to cool, wet environments. The abiotic stress accompanied by drought conditions can predispose susceptible hosts to biotic stress of insect and disease populations. In particular, high elevation subalpine fir (Abies lasiocarpa) have encountered higher than average mortality rates throughout the western United States in association with abiotic and biotic agents. Chapter 2 of this thesis investigated the potential drivers of subalpine fir mortality and determined how climatic factors and site and stand characteristics influenced the presence of mortality and biotic agents. The objectives were to identify factors driving subalpine fir mortality in Colorado and included 1) determine abiotic and biotic factors that directly and indirectly affect subalpine fir mortality, 2) determine factors associated with the presence of D. confusus or Armillaria spp., and 3) determine if climate variables were correlated to subalpine fir mortality or the presence of D. confusus and Armillaria spp. I hypothesized that sites with a higher density (i.e. basal area, trees per hectare, or canopy closure) would experience greater mortality due to decreased growth rates from competition and that D. confusus or Armillaria spp. prevalence would be a function of tree stress (i.e. increased density), elevation, slope, and departures from normal precipitation (i.e. drought), and minimum and maximum temperatures. Stand health monitoring plots found that the most relevant factors to subalpine fir mortality are the presence of D. confusus (p = 0.003) and the percent subalpine fir on plot (p = <0.0001). I identified that stand density (p = 0.0038), elevation (p = 0.0581), and Armillaria spp. (p = 0.0006) were the greatest influences on the presence of D. confusus, while the largest influences on the presence of Armillaria spp. are warmer maximum summer temperatures (p = 0.0136) and the presence of D. confusus (p = 0.0289). Results indicated that increased subalpine fir mortality was attributed to high stand density as a predisposing factor, warming temperatures as an inciting factor, and bark beetles (Dryocoetes confusus) and root disease (Armillaria spp.) as contributing factors. The combination of predisposing, inciting, and contributing factors suggests that subalpine mortality can be defined as subalpine fir decline. Management strategies used to reduce the impact of subalpine fir decline will need to address ways to improve stand health, while decreasing populations of both, D. confusus and Armillaria spp. In regards to Armillaria, the inability to successfully manage the disease using current techniques highlights the need to find novel management strategies… Advisors/Committee Members: Stewart, Jane (advisor), Stromberger, Mary (committee member), Tinkham, Wade (committee member), Trivedi, Pankaj (committee member).

Subjects/Keywords: Climate; Fungi; Subalpine fir mortality; Dryocoetes confusus; Armillaria root disease; Soil Microbiome

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APA (6th Edition):

Lalande, B. (2019). Abiotic and biotic factors influencing western United States coniferous forests. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/195403

Chicago Manual of Style (16th Edition):

Lalande, Bradley. “Abiotic and biotic factors influencing western United States coniferous forests.” 2019. Masters Thesis, Colorado State University. Accessed July 20, 2019. http://hdl.handle.net/10217/195403.

MLA Handbook (7th Edition):

Lalande, Bradley. “Abiotic and biotic factors influencing western United States coniferous forests.” 2019. Web. 20 Jul 2019.

Vancouver:

Lalande B. Abiotic and biotic factors influencing western United States coniferous forests. [Internet] [Masters thesis]. Colorado State University; 2019. [cited 2019 Jul 20]. Available from: http://hdl.handle.net/10217/195403.

Council of Science Editors:

Lalande B. Abiotic and biotic factors influencing western United States coniferous forests. [Masters Thesis]. Colorado State University; 2019. Available from: http://hdl.handle.net/10217/195403

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