Professor University of Northern Colorado, United States
Background/Question/Methods
Climate change has caused increased frequency and severity of disturbance events globally, including widespread bark beetle outbreaks in North America and Europe. Forests recovering from intense outbreaks undergo a series of successional changes that include competitive release of forest-floor vegetation and growth of understory trees. Although bats are known to be impacted by altered habitat structure, how bats are affected by beetle kill and ensuing changes in forest structure remains elusive. Front Range bats in northern Colorado are segregated into foraging guilds including forest, open, edge, and generalist species. I measured overstory and understory vegetative changes, surveyed nocturnal insects using Malaise traps and sweep nets, and deployed Wildlife Acoustics SM2 and SM Mini Bat detectors within severely affected forests (> 50% stand mortality) in various successional stages to quantify how disturbance and recovery alters bat assemblage composition and activity (calls/night) from June to August of 2020 and 2021.
Results/Conclusions
Results from a Non-metric Multidimensional Scaling ordination on data collected in 2020 indicated there is some cohesion of species-specific responses to forest succession according to bat foraging guilds. Activity levels of open habitat foraging species, including Eptesicus fuscus, Lasionycteris noctivagans, and Lasiurus cinereus, are positively correlated with beetle-affected forests with high volumes of decayed coarse woody debris and sites that have higher percent cover of forbs in the understory. These species are not typically found within forest habitats and data on insect abundance and diversity may reveal bottom-up processes influencing food web structure in beetle-affected forests. Additionally, forest structure prior to the outbreak event is contributing to species response patterns as there were low average nightly detections for all bat species in stands with high percent beetle kill and high volumes of newly fallen trees. Additional sites were surveyed in 2021 and those data will be incorporated in this analysis to compare with results from the 2020 dataset. This study will contribute to our understanding of the impacts of climate change on bats in high elevation ecosystems as these habitats are expected to become increasingly important refuges with climate warming at lower elevations.
