Natural and anthropogenic factors influencing the bat community in commercial tree stands in a temperate lowland forest of natural origin (Bialowieza Forest)

In 2011-2017, we examined the ecology of bat assemblages in the commercially used stands of the Bialowieza Forest, Poland. The species composition was analyzed, as well as the relationship between bat activity and distance to buildings and to open waters. The relationship between bat activity and stand age, type of stand (coniferous vs. deciduous), and tree canopy closure (open vs. dense) was also examined. Bat activity was recorded using full-spectrum ultrasound detectors, with subsequent analysis using specialized software. Bats were recorded on eight linear transects. The following species of bats were found: western barbastelle (Barbastella barbastellus), serotine (Eptesicus serotinus), northern bat (Eptesicus nilssoni), common noctule (Nyctalus noctula), lesser noctule (Nyctalus leisleri), soprano pipistrelle (Pipistrellus pygmaeus), Nathusius' pipistrelle (Pipistrellus nathusii), common pipistrelle (Pipistrellus pipistrellus), parti-coloured bat (Vespertilio murinus), and bats from the genus Myotis. Bat activity was affected mainly by the canopy structure along a transect, the number of dead trees, and the age of tree stands. The activity of three from five studied open space aerial foraging bat species (serotine bat, northern bat, and parti-coloured bat) was negatively affected by canopy closure along a transect. Canopy cover was not the most important factor for the other two open space bat species - the common noctule and lesser noctule. Canopy closure was also not a primary factor affecting the edge space foragers like species from this genus Pipistrellus. The activity of Nathusius' pipistrelle was positively correlated with the number of nearby dead trees, whereas the activity of the common pipistrelle was negatively correlated with the upper quartile of trees age. There was no good single environmental variable for the activity of western barbastelle, bats of the genus Myotis and the soprano pipistrelle. However, we found that the activity of western barbastelle and soprano pipistrelle clearly increased among years. The results suggest that commercial forests with limited economic activity are still a suitable environment for forest bats, including rare and endangered species. They also show that the transformation of stands, resulting in anthropogenic open areas, as well as forest roads, allows synanthropic species to penetrate deep into compact stands. We still do not fully know the impact of such a transformation of the fauna on the forest ecosystem, including the impact on vulnerable bat species closely related to forests.