Beauty and the beast: how a bat utilizes forests shaped by outbreaks of an insect pest

Abstract

The consequences of different management strategies following natural disturbances are a matter of global concern. In former production forests around the Northern Hemisphere, the abandonment of intervention, such as removal of dead wood, after outbreaks of bark beetles has been increasingly promoted to regain more natural conditions. However, many focal species of conservation, such as the barbastelle bat Barbastella barbastellus, do not primarily depend on dead wood but might respond indirectly to disturbance-induced changes of forest structural attributes. We investigated the response of B. barbastellus foraging activity and roost selection by combining acoustic surveys, radio telemetry, and airborne light detection and ranging (LiDAR) to characterize B. barbastellus habitat use on different scales. B. barbastellus foraging activity increased with increasing canopy opening. Maternity colonies were recorded exclusively in trees killed by bark beetles. Bats preferred roost trees with a higher volume (m 3 ha À1 ) of live trees in the surrounding, and trees with on average larger diameters than nearby control trees. Our results revealed that outbreaks of bark beetles result in forest structural attributes that are suitable habitat for B. barbastellus. Salvage logging, i.e., the removal of beetleaffected trees, generally deteriorates the positive effects of bark-beetle outbreaks on the foraging and roosting habitat of B. barbastellus. We recommend maintaining snags of large diameter if salvage logging is mandatory.

A Comparison of the Formation Rates and Composition of Tree-Related Microhabitats in Beech-Dominated Primeval Carpathian and Hyrcanian Forests

“…Experts of many forest taxa have pointed out that living trees as well as deadwood provide a number of microhabitats. These include cavities for birds [7], hollow trees with wood molt for specialists such as the hermit beetle (Osmoderma eremita Scopoli) [8], bark shelter as roosting sites for bats [9], rot holes as habitats for lichens and bryophytes [10], water-filled holes in trees (dendrotelms) as habitat for diptera and beetles [11], and the suspended soil used by mites and other small organisms in tree canopies [11]. Moreover, veteran trees often harbour multiple microhabitats, thus providing a functionally rich habitat [12,13], but even snags can host crucial and complementary microhabitats [12,14].…”

Ground-based and LiDAR-derived measurements reveal scale-dependent selection of roost characteristics by the rare tree-dwelling bat Barbastella barbastellus

“…Bats selected roosts in trees that had a more open canopy structure than random trees, as has been observed elsewhere for barbastelles (Russo et al, 2004;Kortmann et al, 2017) and other echolocating tree-dwelling bats (Kalcounis-Ruppell et al, 2005;Fabianek et al, 2015b). Much of this effect, however, may result from the strong selection by barbastelles of roost cavities in standing dead trees that had little or no canopy at all.…”

“…This strong preference for roosting in dead oak trees has also been documented in Germany (Hillen et al, 2010), although roosts in other broadleaved tree types are not uncommon. Use of conifer species by barbastelles has been documented only rarely, such as in dead spruce trees killed by the spruce bark beetle Ips typographus (Kortmann et al, 2017). While the presence of a single suitable roost cavity on a tree may be sufficient, we propose that for barbastelles the overall value of a tree is likely to be positively correlated with the total number of cavities present because (i) more cavities on a tree increases the probability that at least one of them is suitable as a roost site at a particular moment in time, (ii) effort associated with searching for new roost options is reduced, and (iii) it is less risky to relocate to an alternative roost that is close during the day following stochastic events such as degradation of fragile bark plates in poor weather.…”

“…The frequency, type and size of cavities has also been shown to influence roost selection (Russo et al, 2004;Lučan et al, 2009). In addition, bat presence within woodlands has been linked to the ruggedness (Froidevaux et al, 2016) and openness (Russo et al, 2004;Cox et al, 2016;Kortmann et al, 2017) of the upper canopy. Favourable microclimatic conditions may increase roost suitability (Boyles, 2007) and the phenomenon of social thermoregulation driven by roost characteristics indicates that bats do not rely passively on ambient temperature while roosting (Willis and Brigham, 2007;Russo et al, 2017a).…”

“…To date, few studies have characterised the roosting requirements of the barbastelle. Russo et al (2004Russo et al ( , 2010 and Kortmann et al (2017) documented roost preferences in breeding populations inhabiting extensive beech (Fagus sylvatica) and mixed upland forests respectively. Only limited data are available for the species within fragmented broadleaved woodlands at lower elevations that are more typical across the species' Europe-wide range.…”