Beetlemania: Is the bark worse than the bite? Rocky Mountain subalpine forests recover differently after spruce beetle outbreaks and wildfires

Due to the shifting global climate, frequency and severity of disturbances are increasing, inevitably causing an increase in overlapping time space. Bark beetle epidemics wildfires have historically shaped disturbance regimes Western North American forests. Their interactive effects on stand dynamics recovery inadequately studied Picea engelmannii (Engelmann spruce)-Abies lasiocarpa (subalpine fir) dominant forests; understanding these interactions is imperative management health forested ecosystems. This study focuses epidemic Dendroctonus rufipennis (spruce beetle) outbreaks, high-severity fires, subsequent species structural diversity subalpine forest regeneration structure Northern Colorado Southern Wyoming. We compared tree seedling densities composition, surface fuel loading, characteristics across 80 sites that experienced either high mortality from spruce outbreaks (>50% affected basal area), wildfire, post-outbreak wildfire (1–3 years post-outbreak), or no (control). The outbreak span multiple 1996 2017, ultimately comprising a chronosequence beetle-affected stands. Analyses indicate significant loading over time-since-outbreak, as aerial fuels transferred floor following mortality. Tree among control differ significantly burned areas, indicating override repeated regeneration. There was consistent Engelmann survival providing evidence for stable single disturbance. However, fire dominate force determining post-disturbance continued prevalence may prove detrimental persistence spruce-fir species, while promoting shifts toward more drought tolerant (e.g., Pinus contorta). It critical understand identify hazards suppression, implement treatments enhance resilience, potential consequences climate-induced health.