4. The role of deadwood

exceed more than a few dozen individuals in one roost. This pattern was observed in the small European tree-dwelling bat species such as Myotis bechsteinii, Myotis nattereri, Barbastella barbastellus and Plecotus auritus [31]. On the other hand, Nyctalus noctula composes larger groups that occupy large cavities for greater periods of time (unpublished). These diverse behaviours thus imply the need for different conservation strategies. Bat colonies that exploit many cavities are less sensitive to the disappearance of roosts but species that occupy a tree cavity for longer lengths of time are obviously more affected by their disappearance [32, 50]. Thus, the forest manager is faced with the challenge of maintaining a high capacity to accommodate all species throughout his territory. In addition, depending on the forest, the number of cavities can vary considerably. If we consider only woodpecker hollows and fissures on live trees, the number of microhabitats per hectare in a production forest may be greater than 10, while other forests may offer only a very limited or even zero carrying capacity [2, 6, 17, 32]. In

the latter, a loss or alteration of roosts constitutes a major limiting factor for bats.

The literature is rich in identifying the main forest characteristics utilised by most European bat species [2, 6], as forests undoubtedly remain complex environments offering foraging habitats for these species, even when insect populations fluctuate. Studying forest habitats rather than prey abundance can thus contribute to a greater understanding of foraging behaviours [52, 53]. Regardless of the species, certain forest habitats are more attractive than others, broadleaved forests above all [50, 54–59]. It is therefore difficult for a forest manager to apply bat-friendly practices without a precise description of the factors determining habitat selection. According to the numerous studies, forest management causes changes (in terms of the composition and the structure of a forest stand) that are either acceptable or not for bats, as foraging behaviour may be jeopardised [60]. Logging forests for timber production may therefore reduce a colony's ability to sustain itself due to a lack of feeding resources [60, 61].

At the bat community level, the silvicultural parameters that best explain the selection of certain forest habitats are that of structure, composition, and the quantity of foliage among

The maximal diameter of trees, different from stand age (but related) generally translates to a forest stand of overmature trees with the presence of microhabitats [10]. Microhabitats can even serve occasionally as refuge for bats that forage several kilometres from their roosting site, when weather conditions dramatically change [31]. Indeed, old forest stands are the most important habitats for bats as they offer a great potential for roosting [31, 60]. In a diverse forest landscape, bats will predominantly select broadleaved tree stands dominated by oaks and tend to avoid conifers [31]. This is in direct response to the entomological richness

3. Foraging habitats in forests

68 Bats

3.2. Favourable forest stands

other elements beyond the stand itself.

3.1. The importance of forests as feeding opportunities

In Europe few bat species roost in dead trees. Nyctalus leisleri and N. lasiopterus are known to roost from time to time in cavities found on dead or dying trees [29, 73], and Barbastella barbastellus roosts regularly behind peeling bark, especially on snags [27, 28, 74] just like some Myotis and Pipistrellus species. The use of these ephemeral roosts is usually only part of a network of trees surrounding optimal roosting sites [13].

Deadwood constitutes an important support for the development of wood decaying insects with nearly a third of all forest insects directly depending on it [19, 26, 75]. Foraging bats can indeed take advantage of the presence of fresh deadwood by targeting any emerging Coleoptera insects. It is often the case with conifer stands that have been cut and stacked which favour the rapid concentrations of bark beetles (Scolytidae), subsequently attracting opportunistic species of Nyctalus, Eptesicus and Pipistrellus (Figure 1) [76, 77]. More widely, the richness of bat species has been found to be positively correlated to the volume of deadwood, either lying or standing, greatly increasing when deadwood quantity exceeded 25 m3 /ha [78]. This relation can be explained by deadwood-dwelling preys or by changes in the forest structure, due to openings created by dead trees that are favourable for edge-hawkers such as Pipistrellus spp., Eptesicus

serotinus and Nyctalus leisleri. On the other hand, gleaners that pick up insects from the substrate e.g. leaves (most of Myotis and Plecotus) prefer to forage within the foliage [59, 70, 79–81] and do not dwell in areas with large quantities of deadwood, selecting above all forest

Bat Conservation Management in Exploited European Temperate Forests

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Bats respond differently to roosts as well as foraging habitats (or home ranges) according to their reproductive state. The energy needs of reproductive females are such that they become a lot more demanding than the other individuals [82]. Myotis bechsteinii and Plecotus auritus which are two ecologically and morphologically similar species illustrate this different use of available resources influenced by their reproductive status. Pregnant females of M. bechsteinii have smaller home ranges than non-reproductive females, change roost frequently often selecting roosts high in the trees and entering into a torpor when meteorological conditions deteriorate [31, 82]. Then, lactating females and young forage over high-quality habitats while non-reproductive females forage in lower-quality habitats such as conifer or young broadleaved stands. Social exchanges take precedence when selecting roosts, with colonies settling in large cavities without much vegetation clutter at the entrance allowing for several individuals to leave and enter the roost at a time [32]. On the contrary, pregnant females of P. auritus use large home ranges and can roost alone in a tree far from the main colony for several days. Lactating females systematically stay within the colony, foraging in good-quality habitats close to the cavity. Non-reproductive females use the same types of habitats but forage further from the colony [31]. Thus, the conservation of a network of cavities is clearly crucial for both species, including the preservation of woodpecker hollows at elevated positions on trees for M. bechsteinii. The same advice applies to other species with behavioural differences in the utilisation of tree cavities and habitat selection in Europe such as Myotis daubentonii [64] and Myotis nattereri [31], and on other continents, such as Myotis septentrionalis [65], Eptesicus fuscus [74], Chalinolobus tuberculatus [70, 83] and Mystacina

habitats that are cluttered by vegetation [78].

tuberculata [84].

6.1. The impacts of silviculture

5. Individual responses of bats to habitat selection

6. Bat conservation in the context of forest management

Regardless of the type of silvicultural practice undertaken in forests around the world, biodiversity will be affected. Harvest exclusion areas or setting aside reserves within production forests constitute sites that are richer in terms of species present, whereas timber plantations with more economically profitable methods employed, notably short rotation forestry, are the most impacting of approaches [1, 26, 71]. For bats, silvicultural logging reduces food resources, destroys breeding sites, and can kill individuals or colonies when trees are felled [2, 5, 6, 71]. Females of Plecotus auritus have been shown to entirely avoid forests recently logged during lactation periods even if mature trees have been preserved [32]. The same avoidance has also

Figure 1. The spatial distribution of foraging bats in a forest stand. Gleaners (Myotis and Plecotus) forage within the foliage of the trees and around shrubs and bushes in the understory, whereas hawkers (Nyctalus, Eptesicus, Barbastella and Pipistrellus) are distributed above and under the canopy (a). When a tree dies, (b) a space free of vegetation forms. This clearing is generally avoided by gleaners and possibly exploited by hawkers where the space is not too cluttered by dead branches. Barbastella barbastellus may take advantage of any peeling bark for potential diurnal roosts. Once the dead tree has fallen, (c) hawkers distribute at the top of the clearing. The forest gap allows light to penetrate to the ground level, favouring the development of low vegetation. Certain gleaners (Myotis nattereri and Plecotus auritus) take advantage of this opportunity by foraging in the understory while others (Myotis myotis) require bare ground, and Myotis bechsteinii continues to exploit the foliage of the canopy. Bb: Barbastella barbastellus; Es: Eptesicus serotinus; Mb: Myotis bechsteinii, mm: Myotis myotis; Mms: Myotis mystacinus; Mn; Myotis nattereri; Nl: Nyctalus leisleri; Nn: Nyctalus noctula; Pa: Plecotus auritus; Pk: Pipistrellus kuhlii; Pp: Pipistrellus pipistrellus.

serotinus and Nyctalus leisleri. On the other hand, gleaners that pick up insects from the substrate e.g. leaves (most of Myotis and Plecotus) prefer to forage within the foliage [59, 70, 79–81] and do not dwell in areas with large quantities of deadwood, selecting above all forest habitats that are cluttered by vegetation [78].
