Temperature is positively associated with tree mortality in California subalpine forests containing whitebark pine

Whitebark pine (Pinus albicaulis Engelm.) is a keystone high-elevation tree species occurring across much of western North America, yet it has been listed as threatened under the US Endangered Species Act due to rapid population declines and extensive ongoing pressures from white blister rust (Cronartium ribicola), mountain beetle (Dendroctonus ponderosae), increasing temperature aridity associated with climate change. Past research shown that whitebark mortality more likely in hotter drier sites, but no broad-extent analyses spanning multiple ecoregions have directly quantified relationship between probability its environmental drivers at fine spatial scale. To address this gap, we used spatially continuous high-resolution (30 m) maps California produced by remote sensing-based change detection algorithm, developed generalized additive models explain variability using relevant biophysical variables. We found maximum daily was strongly positively intensity also generally intense sites greater solar exposure (e.g., south-facing slopes). Our results support interpretation warms increases, populations “trailing edge” (i.e., hot, dry) are most vulnerable. The relationships quantify will aid identifying locations environments greatest risk future well those serve refugia.