Drivers of Mortality, Herbivory, and Disease in Whitebark Pine Across Climatically Heterogeneous Landscapes
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Authors
Lloyd, Rachel L
Issue Date
2025
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Many tree species globally are in decline, driven by environmental stress from a combination of biotic threats and climate change. Rising temperatures, shifting precipitation patterns, and increasing drought—hallmarks of a changing climate—are weakening tree defenses and amplifying vulnerability to insects and disease. In forested ecosystems, these stressors rarely act alone: interactions among climate, herbivores, and pathogens often create compounding effects that accelerate tree mortality. Understanding how these drivers operate in concert across heterogeneous landscapes is crucial for anticipating and managing forest decline. In light of escalating threats from climate change, insects, and pathogens, this study addresses the critical decline of whitebark pine (Pinus albicaulis; WBP), an imperiled keystone species in subalpine ecosystems across western North America. I used a plot network spanning diverse climatic and topographic gradients to examine how environmental stressors, alongside herbivore and pathogen interactions, influence WBP mortality. My results indicate that herbivory by mountain pine beetle (Dendroctonus ponderosae) and infection by the exotic pathogen, white pine blister rust (Cronartium ribicola) significantly impacted WBP mortality, with complex interactions among biotic and abiotic forces. Warmer spring temperatures and reduced water availability were key abiotic drivers linked to elevated beetle activity and increased mortality. These findings demonstrate that multiple stressors interact to shape the vulnerability of WBP, underscoring the urgency of conservation measures as this species faces intensifying threats. Understanding these dynamics is essential for developing targeted and effective forest management strategies.