Outbreaks of Douglas-Fir Beetle Follow Western Spruce Budworm Defoliation in the Southern Rocky Mountains, USA

Changes in climate are altering disturbance regimes forests of western North America, leading to increases the potential for events overlap time and space. Though interactions between abiotic biotic (e.g., effect bark beetle outbreak on subsequent wildfire) have been widely studied, multiple disturbances poorly understood. Defoliating insects, such as spruce budworm (WSB; Choristoneura freemanni), suggested predispose trees secondary colonization by beetles, Douglas-fir (DFB; Dendroctonus pseudotsugae). However, there is little quantitative research that supports this observation. Here, we asked: Does previous WSB damage increase likelihood DFB (Pseudotsuga menziesii) Southern Rocky Mountains, USA? To quantify areas affected then DFB, analyzed Aerial Detection Survey data from 1999–2019. We found a presence followed defoliation more often than expected under null model (i.e., random distribution). With change intensify some disturbances, an understanding insect outbreaks important forest management planning, well improving our change.