Whitebark pine persistence potential highly variable following disturbance in the Intermountain West, USA

Widespread mortality poses a major conservation challenge for foundation species whitebark pine (Pinus albicaulis Engelm.). We assessed whitebark pine forest structure, composition, and persistence potential in Idaho and Nevada, USA following mountain pine beetle (MPB), wildfire, and no recent disturbance by comparing overstory and regeneration relative abundances, classifying post-disturbance communities, and gauging persistence via residual mature trees and seedlings. Wildfire mortality spanned all species and sizes and exceeded MPB mortality, which was limited to larger pines. Disturbance regulated competing canopy species, with subalpine fir trees decreasing following fire and rising following MPB; however, subalpine fir relative regeneration abundance was disproportionately greater following fire and MPB. Non-native white pine blister rust disproportionately impacted small trees in 48% of plots. Whitebark pine persistence metrics of live overstory for cone production (basal area ≥5 m2 ha-1) and successful regeneration (≥250 seedlings ha-1) occurred on 23% of plots. A subset (14%) exceeded overstory but not seedling metrics, while 33% exceeded seedling but not overstory metrics. Roughly 30% of plots did not meet minimum persistence thresholds. Sufficient overstory was predominantly on undisturbed sites, with satisfactory seedling densities after MPB. Consideration of forest composition and persistence metrics will be valuable for prioritizing conservation efforts.