Patterns of woodboring beetle activity following fires and bark beetle outbreaks in montane forests of California, USA

Abstract

Background: Increasingly frequent and severe drought in the western United States has contributed to morefrequent and severe wildfires, longer fire seasons, and more frequent bark beetle outbreaks that kill largenumbers of trees. Climate change is expected to perpetuate these trends, especially in montane ecosystems,calling for improved strategies for managing Western forests and conserving the wildlife that they support.Woodboring beetles (e.g., Buprestidae and Cerambycidae) colonize dead and weakened trees and speedsuccession of habitats altered by fire or bark beetles, while serving as prey for some early-seral habitatspecialists, including several woodpecker species. To understand how these ecologically important beetlesrespond to different sources of tree mortality, we sampled woodborers in 16 sites affected by wildfire or barkbeetle outbreak in the previous one to eight years. Study sites were located in the Sierra Nevada, ModocPlateau, Warner Mountains, and southern Cascades of California, USA. We used generalized linear mixedmodels to evaluate hypotheses concerning the response of woodboring beetles to disturbance type, severity,and timing; forest stand composition and structure; and tree characteristics.Results: Woodborer activity was often similar in burned and bark beetle outbreak sites, tempered by localizedresponses to bark beetle activity, burn severity, tree characteristics, and apparent response to ignition date.Larval woodborer activity was inversely related to bark beetle sign within a sampling quadrat, was higher onpines, and—in burned sites—was higher on the south-facing sides of smaller trees. Adults—especiallybuprestids—were more abundant where burn severity was higher. Fires with intermediate ignition datesduring the study period supported higher rates of larval woodborer activity and higher numbers of adultbuprestids as well as cerambycids in the genus Monochamus Dejean 1821.Conclusions: Woodboring beetle abundance was related to bark beetle activity, burn severity, treecharacteristics, and ignition date. Considering these patterns when managing disturbed forest stands couldyield improved outcomes for wildlife, including species that prey on woodboring beetles. We also reportedpreliminary evidence that the current trend toward more frequent wildfires might not stimulate largerwoodboring beetle populations if those fires increasingly occur outside the historical fire season.

Citation

Ray, Chris; Cluck, Daniel R.; Wilkerson, Robert L.; Siegel, Rodney B.; White, Angela M.; Tarbill, Gina L.; Sawyer, Sarah C.; Howell, Christine A. 2019. Patterns of woodboring beetle activity following fires and bark beetle outbreaks in montane forests of California, USA. Fire Ecology. 15: 21. https://doi.org/10.1186/s42408-019-0040-1.