Following the damage: Increasing western barbastelle bat activity in bark beetle infested stands in Bialowieza Primeval forest

Natural forest disturbances are increasingly common due to ongoing climate changes but their impact on most of forest organisms is poorly studied. Here we investigate the link between spruce bark beetle Ips typographus outbreak in 2011-2017 in Bialowieza Primeval Forest (Poland) and activity of a forest bat of conservation concern: the western barbastelle Barbastella barbastellus. Bats were surveyed by recording ultrasound signals on 8 transects (3 km each) in a mixed coniferous and deciduous forest with a different share of Norway spruce. The activity pattern of bats was found to correlate with the number of bark beetle infested Norway spruces in the following years within a 1 km buffers of the transects (339,354 trees in total) using generalised additive mixed models. We demonstrated that the number of bark beetle infested spruces was a positive predictor of barbastelle activity largely with 1- and 2-year lags: number of spruces infested in a year correlates with bat activity one and two years later. This latency period most likely mirrors the decomposition process in standing dead spruces. We suspect that the massive appearance of dying Norway spruces provides the barbastelle with roosting sites under the bark and may lead barbastelle to colonize spruce stands otherwise rarely occupied by this species. It cannot be excluded, however, that other mechanisms (e.g. increased food biomass or availability) also drive the barbastelle to colonize stands infested by bark beetle. Our findings suggest that salvage logging and dead spruce removal, routinely implemented in stands infested by bark beetle, including Bialowieza Primeval Forest, may negatively impact western barbastelle population.

Automated summary

The study found a positive correlation between the number of Norway spruces infested by spruce bark beetles and the activity of western barbastelle bats, with a lag of 1-2 years. This is likely due to the decomposition process in standing dead spruces. Salvage logging and dead spruce removal in stands infested by bark beetle may negatively impact the western barbastelle population.