Bat activity and diversity in a temperate old-growth forest - Influence of horizontal and vertical structural heterogeneity on the bat assemblage of the Belovezhskaya Pushcha, BelarusDissertation
Datum der mündl. Prüfung:2022-01-13
Betreuer:Prof. Dr. Christoph Leuschner
Gutachter:Prof. Dr. Niko Balkenhol
Gutachter:Dr. Markus Dietz
EnglischThere are two different options to manage forests in the era of global climate warming, with partly opposing inferences. One is to reduce management or abandon it, as undisturbed forest ecosystems effectively store carbon and usually are relatively resilient against disturbance effects (Naeem 1998, Peterson et al. 1998, Bengtsson et al. 2000). Leaving forests untouched thus is an efficient climate change mitigation option. Another option is to reduce CO2 emissions by the replacement of fossil fuels through timber-derived raw materials. Expanded use of forest products however entails a more intense forest management. These two opposing management perspectives need to be intertwined to define a compromise leading to truly climate-smart forestry (Verkerk et al. 2020). Most temperate bats rely on forested habitats for hunting or roosting. As three-dimensionally moving animals, they are especially sensitive to habitat alterations and are directly affected by forest management. Indeed, vegetation structure and species composition determine species-specific habitat use, arthropod prey occurrences and the availability of natural tree roosts. Forest bats are thus sensitive indicators of forest biodiversity. The present thesis aimed at analysing horizontal and vertical activity patterns of temperate forest bats in a coherent temperate old-growth forest. The Belovezhskaya Pushcha (BP) lowland woodland complex can serve as a reference for the study of old-growth dynamics through the number of untouched forest patches present and its size stretching beyond the Polish-Belarusian border. Bat diversity in unmanaged stands was compared to managed stands in the Economic Activity Zone of the Belovezhskaya Pushcha National Park (BPNP). Moreover, species-specific preferences for natural tree roost attributes were extracted in a meta-analytical framework combining own data with datasets from literature. We used automatically recording devices (batcorder) whose omnidirectional ultrasonic microphones are triggered by calls of echolocating or hunting bats. Bats were monitored simultaneously in natural canopy gaps and the adjacent forest interior within two forest communities in the Strictly Protected Zone of BP, namely Tilio-Carpinetum (broadleaved) and Querco-Pinetum (mixed-coniferous) stands. The impact of management was analysed by acoustically sampling managed Peucedano-Pinetum stands in the Economic Activity Zone of BPNP. A vertical batcorder setup in three forest heights analysed vertical stratification patterns of forest bats in canopy gaps and the adjacent forest interior. Bat activity in canopy gaps was slightly higher for edge-space foraging bats compared to the forest interior, while bat richness was higher in gaps only in the species-poor mixed-coniferous stands. Vertical stratification was more pronounced in the forest interior than in canopy gaps, and vertical forest use clearly showed species-specific and seasonal differences. Bat diversity in BPNP was impacted by management with especially evenness being lower in homogenized human-altered managed coniferous forests. The activity levels of four strict forest species in the forest interior were negatively influenced by tree basal area (B. barbastellus, P. pygmaeus, M. brandtii) and positively influenced by the proportion of broadleaved trees (P. pygmaeus, M. brandtii, M. nattereri). B. barbastellus and M. nattereri were furthermore found to be tree roost specialists. While B. barbastellus favours loose bark of dead trees as day roosts, M. nattereri preferentially roosts in cavities or crevices in vital broadleaved trees. Near-natural broadleaved forests are important habitats for temperate forest bat assemblages. The emulation of canopy gaps as a forest management strategy creates structurally heterogeneous forest stands that support a higher bat diversity through an increase in physical niches and foraging opportunities. Both the retention of snags and of large-sized vital trees offer essential roosting opportunities for forest bats and need to be integrated in close-to-nature forest management practices.
Keywords: Bialowieza; bat ecology; old-growth forests; forest bats; three-dimensional bat activity; forest structural heterogeneity; acoustic bat inventory; forest gaps