Subalpine fir decline is a poorly understood phenomenon that has killed trees across millions of hectares in western North America with unknown consequences for future forest resilience. Causes of the tree mortality are poorly understood but include the western balsam bark beetle.
We used broad-scale geospatial data analysis combined with small scale forest stand and individual tree data to examine the relative importance of factors driving subalpine fir decline.
At the sub-continental scale, the extent of subalpine fir mortality was associated with prior drought. Moist topographic conditions were drivers at regional scales. At smaller stand and tree scale, the probability of mortality was influenced by tree diameter and proximity to previously dead trees.