Overlapping outbreaks of multiple bark beetle species are rarely more severe than single‐species outbreaks

Biotic disturbances that overlap in space and time may result important shifts forest structure composition, with potential effects on many ecosystem services. Starting the late 1990s, outbreaks of multiple bark beetle species caused widespread mortality three co-occurring conifer ca. 40,000-km2 subalpine zone southern Rocky Mountains (SRM), USA. To better understand implications such outbreaks, our goal was to determine if overlapping greater tree than single-species stands susceptible host species. We mapped stand susceptibility spruce (SB, Dendroctonus rufipennis), mountain pine (MPB, ponderosae), western balsam (WBBB, Dryocoetes confusus) by combining aerial survey data composition variables a random modeling framework. Then, we used existing maps cumulative from beetles investigate extent severity 1999 2019. found 46% two or more studied hosts species—Engelmann (Picea engelmannii), lodgepole (Pinus contorta var. latifolia), fir (Abies lasiocarpa)—were (25% all sampled stands). Of those stands, 31% experienced Stands affected both MPB SB had higher one alone, though were uncommon (<4% No other combinations increased above levels outbreaks. Thus, contrary expectations, rarely severe SRM. This suggests diverse communities buffer against most even during warm, dry conditions.