Open access peer-reviewed chapter

Bat Conservation Management in Exploited European Temperate Forests

Written By

Laurent Tillon, Joseph Langridge and Stéphane Aulagnier

Submitted: October 5th, 2017 Reviewed: December 19th, 2017 Published: July 4th, 2018

DOI: 10.5772/intechopen.73280

From the Edited Volume

Bats

Edited by Heimo Mikkola

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Abstract

Forests offer important refuge to bats by providing attractive roosting and foraging habitats. Their conservation is a major responsibility of forest managers. The use of tree cavities by bats in forests depends on the specific demands of each species, with a large range of different types of microhabitats utilised, from degraded cavities such as peeling bark to healthy hollows in live trees ensuring the temporal stability of the habitat. The conservation of tree-dwelling bats should not be dissociated from their fission-fusion behaviour which involves the use of many different roosts. Conservation measures must therefore take into account forest habitats suitable for feeding and in particular, forest parameters such as structure, composition, vegetation and foliage, among other elements such as deadwood, all upon which the forest manager can intervene. Acting in favour of bats requires close consideration of their complex individual responses concerning roost selection and foraging habitat selection, which is largely dictated by the reproductive status of individuals. Thereafter it is possible to evaluate the impact of wood harvesting on bats and to infer silvicultural conservation measures. The implementation of recommendations must then subsequently be based on a strong involvement on the part of the forest manager.

Keywords

  • Chiroptera
  • tree cavities
  • roost network
  • foraging habitat
  • deadwood
  • forest management

1. Introduction

In Europe, forests cover an area of approximately 4.5 million km2, from the boreal forests of Scandinavia and Russia to the forests of the Mediterranean, including natural forests, plantations and intensive production forest systems [1]. They constitute a habitat particularly attractive to bats by providing the potential for roosting and foraging. Since the 1990s, conservation biologists have considered the forest as one of the most important refuges for biodiversity, in particular for a number of terrestrial mammals and bats [1, 2, 3]. Moreover, forests probably represent one of the least altered habitats across the continental landscape. Thus, forest managers must engage in implementing favourable management strategies for these species [2, 4]. Our knowledge about bats was still largely considered fragmentary at the beginning of the twenty-first century, outlined in a review on the relationships between bats and forests in North America [5]. In Europe, studies have multiplied in recent years promoting a greater understanding of the impacts of forest management on bats. This path to knowledge has revealed the relationships between bats, roosting sites, and foraging habitats across a number of settings, from natural forests, to intensive production forests, and to plantations with exotic species [6]. Unsurprisingly, bat species abundance and richness is considerably higher in forests that resemble a natural state [2, 7], which is probably in response to a greater presence of certain habitats related to the abandonment of logging practices, such as deadwood and tree cavities [8, 9, 10]. However, provided society’s demand for wood products persists, the sometimes intensive exploitation of forests will continue to have a strong impact on biodiversity. In Europe, some sites already have high-quality favourable habitats at the landscape scale, principally in forests, and contribute markedly to the concentration of bats, especially the most specialised species [8]. These sites have consequently been included in the Natura 2000 network and are subject to contractual or regulatory management measures favouring biodiversity at the landscape scale. However, recent studies on certain forest habitats within the Natura 2000 network, notably beech (Fagus sylvatica) forests show that the measures implemented are slow to produce significant positive results for bats [9]. This can be explained by the slow evolution of forests with tree microhabitats taking considerable time to form, particularly in beech stands [10]. Hence, the integration of biodiversity issues should not wait until results are convincing before engaging in concrete conservation management actions as, in any case, they are typically slow at being implemented without strong regulatory measures. In forests primarily destined for logging, two key questions arise: towards which conservation strategy it is necessary to direct managers? And, is the setting aside of certain areas a sufficient response for bats? Thus, reconciling the issues related to both the exploitation of wood and the conservation of bats, accounting as much for roosts as for their foraging habitats is a true challenge for society [11].

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2. Bat use of tree cavities

2.1. Types of roosts

In forests exploited for timber production, the number of available trees with cavities that can be used by bats are generally low, as young vigorous trees are favoured for wood production [12, 13]. The formation of cavities is very slow. Less than 1% of Quercus roburtrees of 100 years old or less formed a cavity, compared to 50% of trees aged between 200 and 300 years old and all trees older than 400 years [14]. In forests, time is therefore an essential component to consider. Among cavities, only 9% were used by bats in a lowland temperate forest [15], corresponding to only 1% of trees sufficient in size to possess a cavity [16]. Because bats are incapable of creating their own roosts, they must rely on cavities created by wind, frost, the natural degradation of wood [17, 18], or by other organisms such as saproxylic insects and birds [19, 20]. The selected cavities must provide effective protection against predators and adverse weather conditions (wind, rain, and extreme temperatures) while also supporting social exchanges between individuals [17, 21, 22]. Cavities are generally more numerous on broadleaved trees than on conifers, and are not only favoured by the vitality and diameter of trees but also by the time elapsed since the last harvest at the forest stand level [23, 24]. In Mediterranean hardwoods such as Quercus ilex, tree diameter is the best predictor for the formation of microhabitats such as woodpecker hollows, insect holes and peeling bark [24]. Given that cavity-bearing trees are generally scarce in timber production forests, microhabitat density including bat-usable cavities is thus favoured in exclusion areas/set-asides, irrespective of the silviculture stage [23, 24, 25, 26].

Bat colonies use tree cavities. As a result, their reproduction is all the more favoured if the forest area they occupy has a high density of potential roosting sites [27]. However, the majority of European forests are subject to the effects of timber harvest, presenting a considerable constraint to the biodiversity associated with tree microhabitats. This therefore constitutes the first major pressure facing bats in forests [2, 12, 13]. Any conservation strategy at the regional scale must therefore take into account the bat species present and the available cavities. Furthermore, the type of cavity selected indeed varies according to the species, Barbastella barbastelluspreferentially selects cavities such as peeling bark on deadwood, in particular snags [13, 28], that are well exposed to sunlight. This prerequisite contributes to maintaining the necessary heat inside the roost especially when rearing young, consequently reducing the physiological demands linked to thermoregulation [27]. Other species, notably Nyctalus leisleriand Myotis brandtii,also show preferences for relatively degraded cavities, rather ephemeral and sometimes even distinctly exposed, despite the potential risk of predation [29, 30]. However, most tree-dwelling bat species across different genera select roost types other than defoliating bark, principally woodpecker hollows and narrow fissures/cracks which represent more sustainable cavities, and which are generally protected from terrestrial predators. Maternity colonies target a large available volume in the cavity, situated on a healthy part of the tree and as high as possible; over time a preference for live trees is evident since they ensure better thermal regulation within the roost during periods of extreme weather [15]. Most bat species, for instance, Myotis bechsteinii, M. brandtii, Plecotus auritus, Vespertilio murinusand Pipistrellussp. select healthy large diameter trees [16, 30, 31]. Furthermore, whatever the selected roost, the closure of the forest environment allows individuals to take advantage of the foliage and the decline in luminosity to begin foraging earlier and return later all the while sheltered from potential predators [32]. This emergence behaviour has been demonstrated notably for Barbastella barbastellus[33], Myotis nattereriand Plecotus auritus[31]. In contrast, Nyctalus noctulaand N. leislerihave a less manoeuvrable flight not allowing for cluttered areas at the entrance/exit of roosts. They seek out a compromise between the need to avoid predators and the need to take maximum advantage of available solar radiation during the day to minimise energy expenditure concerning the warming of breeding roosts. The cavities selected are thus situated high in trees in order to limit the predation risk where the canopy foliage is sparser favouring the insulation of roosts [34].

With increasing pressure for timber products in European forests, tree-dwelling bats must demonstrate sufficient plasticity in their behaviour in order to adapt to the challenge of a fluctuating availability of suitable roosts. Nyctalus noctulaand N. leisleri,which preferentially use old trees of large diameters [29], can adapt to using young trees [12]. Myotis nattererimay target woodpecker hollows but is also known to utilise narrow fissures in small diameter trees such as Birch, Betulasp. However, this capacity to adapt can have its limits. In New Zealand, certain colonies of Chalinolobus tuberculatusappear no longer able to produce enough young to maintain colony numbers when usable cavities are lacking and food resources are reduced following forest exploitation [35]. Hence, management can affect the capacity of forests to produce the required roosts for maternity colonies. As a result roosts clearly become a limiting factor for bats.

2.2. Fission-fusion behaviour

Bat colonies select cavities of which the size and the type govern the structure and the numbers of the group occupying them. Consequently, pregnant females of Myotis bechsteiniimay target small cavities high in trees limiting the risk of predation, and then select large cavities with a significant volume that can shelter larger groups at lower sites when they are lactating. In contrast, pregnant females of Plecotus auritusselect a diversity of cavities in order to use smaller roosts after the birth of young (therefore limiting the size of the group) [31]. Most available cavities in forests have a reduced internal volume. Indeed, cavities of large volume take longer to form and are mainly found on old trees of large diameters [36, 37]. In order to respond to such ecological constraints, i.e. the limited number of tree microhabitats of suitable volume, forest-dwelling bat populations split into subgroups, demonstrating an exchange of individuals on a daily basis [38, 39]. Thus, groups divide and disperse each night (fission) then form new groups the following day, reorganised in accordance to the specific rules of each species, often selecting a new roost (fusion) [38].

Fission-fusion may limit the risk of parasitism [38, 40, 41], as tree cavities being confined spaces are conducive to the development of micro-organisms linked to wood degradation [19] and maintain an increase in humidity and heat favouring the development of bat parasites. In mammals, parasite density decreases with the frequent changing of rest sites [42]. For bats, this phenomenon outlines the importance of using a large number and diversity of cavities. The changing of roosts also allows bats to limit the risk of predation, as predators would no longer know which cavity exit to prowl [41]. Though, the frequency in which bats switch roosts is more dependent on meteorological conditions and the individuals’ reproductive status [31, 43]. A disadvantage is that over time, these repeated fissions can lead to a loss of familiarity among individuals as life in a fission-fusion society imposes constant regroupings of different individuals [17, 22, 44, 45]. Myotis bechsteiniicounteracts this problem with the oldest females organising the colonies around a few lineages or familiar groups that have maintained social links for more than 5 years [45]. In every example, fission-fusion behaviour involves the presence of a close network of primary roosts surrounded by “satellite” roosts, with the gradual and regular establishment of new roosts, especially when the oldest ones begin to degrade [46].

2.3. Roost networks

The turnover of roosts in relation to fission-fusion dynamics occurs, on average, every 2 or 3 days (Table 1). As a result, a substantial quantity of available cavities within the home range of a given bat colony is essential. The frequency in which bats change roost is largely influenced by the individuals’ reproductive status, as outlined above. Females often change roosts when pregnant and tend to stay longer in the same cavity when lactating because maintaining higher temperatures, which is crucial, is energy-intensive for animals [22]. Accordingly, Nyctalus lasiopteruschanged the cavity every 2.52 ± 0.74 days before the birth of young but stayed 4.88 ± 1.91 days in a cavity after birth [47]. Similarly, pregnant Barbastella barbastellusswitched roosts every 2.6 ± 1.6 days, whereas lactating females stayed in the same cavity for up to 9.4 ± 1.8 days [27]. Conformably, reproductive females of the species Myotis bechsteinii, M. nattereriand Plecotus auritusstayed longer in their roosts than non-reproductive females [31].

SpeciesDuration in number of daysReference
Chalinolobus tuberculatus(1)1.7 ± 2.0[51]
Mystacina tuberculata(1)5.6 ± 6.9[52]
Eptesicus fuscus(2)1.7 ± 0.7[53]
Myotis septentrionalis(2)1.6 ± 0.5[54]
1.26 ± 0.40 to 1.20 ± 0.49[55]
Myotis bechsteinii(3)2.1 ± 1.1[56]
1.3 ± 0.8[31]
Myotis nattereri(3)1.2 ± 0.6[31]
Barbastella barbastellus(3)2.6 ± 1.6[27]
2.0 ± 1.8[28]
Nyctalus lasiopterus(3)2.68 ± 0.82[50]
Plecotus auritus(3)1.4 ± 0.8[31]

Table 1.

Average duration of presence (± standard deviation) in one roost by a number of forest-dwelling bat species demonstrating a fission-fusion society, in New Zealand (1), North America (2) and in Europe (3).

Myotis bechsteiniimay exploit more than 300 different cavities in the same year [31] and is able to use more than 15 different zones for roosting purposes [48]. This is in line with other species such as Myotis nattereri, Barbastella barbastellusand Plecotus auritus[13, 28, 31]. In New Zealand a colony of Chalinolobus tuberculatusused more than 300 cavities and re-used only 48% over the course of a year [49]. Conversely, Mystacina tuberculataselected a small number of roosts but was likely to stay for longer periods of time [50], demonstrating a much higher loyalty to its chosen cavities. Roosts should be voluminous in order to accommodate a large number of individuals (310 ± 88.1 on average) [51]. However, for the majority of species, colonies do not 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 barbastellusand Plecotus auritus[31]. On the other hand, Nyctalus noctulacomposes 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.

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3. Foraging habitats in forests

3.1. The importance of forests as feeding opportunities

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, 55, 56, 57, 58, 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].

3.2. Favourable forest stands

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 other elements beyond the stand itself.

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 associated with these tree species [62]. Native Quercusspp. have the highest number of dependent insect species including various orders of saproxylics as well as defoliators (Coleoptera, Lepidoptera, Heteroptera, etc.). They are followed by Betulaspp. which can sometimes have a greater number of individuals present but have less taxonomic groups associated with Salixspp., Crataegusspp., Prunusspp., and Populusspp. The first conifer species is Pinus sylvestrisbefore Fagusspp. and Picea abies[63]. Moreover, the more the forest habitat is diversified, the more the insects’ emergence is spread over time. For example, defoliators commonly emerge at different times in accordance with shade-tolerant and shade-intolerant trees [19]. In addition, a diversification of accompanying tree species and a strong presence of forest gaps in mature conifer plantations can have a positive impact on bat activity [64, 65], with bats contributing significantly to the control of insect pests in forests [66]. Furthermore, a higher density of vegetation and a greater heterogeneity from the ground to the canopy appear to increase bat species richness. Myotis bechsteiniiprincipally forages within the dense canopy [31, 67] whereas Myotis myotisis a specialist of bare ground-dwelling prey [68]. Indeed, a complex structure of the forest with dense foliage, depressions, protuberances, and other ecotones is favourable to the development of different thermal and hygrometric conditions, the source of high entomological production [23, 69]. This can result in a higher activity of hawkers and gleaners [59, 70, 71, 72]. The latter forage for prey by gleaning insects from the substrate in dense foliage, while the former requires open spaces, such as forest clearings, paths, corridors, and edges even though they mainly hunt insects dependent on foliage [59, 70, 71]. Hence, the more diverse a forest is in composition, structure, and stratification, the higher bat species abundance and species richness will be [2]. Finally, additional forest environments such as streams and ponds, which present drinking sites for all individuals, also favour the occurrence of forest-dwelling bats [6, 7].

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4. The role of deadwood

In Europe few bat species roost in dead trees. Nyctalus leisleriand N. lasiopterusare known to roost from time to time in cavities found on dead or dying trees [29, 73], and Barbastella barbastellusroosts regularly behind peeling bark, especially on snags [27, 28, 74] just like some Myotisand Pipistrellusspecies. 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 Coleopterainsects. 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, Eptesicusand 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 Pipistrellusspp., Eptesicus serotinusand Nyctalus leisleri. On the other hand, gleaners that pick up insects from the substrate e.g. leaves (most of Myotisand Plecotus) prefer to forage within the foliage [59, 70, 79, 80, 81] and do not dwell in areas with large quantities of deadwood, selecting above all forest habitats that are cluttered by vegetation [78].

Figure 1.

The spatial distribution of foraging bats in a forest stand. Gleaners (MyotisandPlecotus) forage within the foliage of the trees and around shrubs and bushes in the understory, whereas hawkers (Nyctalus,Eptesicus,BarbastellaandPipistrellus) 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 barbastellusmay 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 nattereriandPlecotus auritus) take advantage of this opportunity by foraging in the understory while others (Myotis myotis) require bare ground, andMyotis bechsteiniicontinues 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.

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5. Individual responses of bats to habitat selection

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 bechsteiniiand Plecotus aurituswhich are two ecologically and morphologically similar species illustrate this different use of available resources influenced by their reproductive status. Pregnant females of M. bechsteiniihave 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. auritususe 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 tuberculata[84].

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6. Bat conservation in the context of forest management

6.1. The impacts of silviculture

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 auritushave been shown to entirely avoid forests recently logged during lactation periods even if mature trees have been preserved [32]. The same avoidance has also been observed in juveniles of Myotis bechsteiniiand Myotis nattereriprobably due to the decrease in the volume of foliage, which is an important source of insect production for these species [31]. More generally, logging forests for timber induces a net loss of prey-bearing mature broadleaves causing an immediate reduction in food resource. Therefore, bats are forced to move to new habitats next to their previous foraging grounds that are already occupied by other individuals, reducing the carrying capacity of the milieu. The silvicultural harvesting of mature trees that possess cavities inevitably leads to a reduction of the total number of roosts available to bats. Even if the natural ageing of trees continues and is accompanied by the gradual formation of new cavities, principally by woodpeckers, the setting aside of areas of unlogged mature forest to protect habitat diversity must still be maintained in order to ensure the temporal and spatial continuity of bat colonies [2, 6, 31]. Indeed, only harvest exclusion areas where the natural forest cycle is allowed to continue without the intervention of man represent truly ideal habitats for bats [80]. However, strict protection obviously remains an unrealistic measure across the European forest scale, implying a need for other forest management strategies.

6.2. Forest management orientations in favour of bats

Given the major differences in the ecological functioning of forest habitats, i.e. different compositions and structures, combined with a diverse range of silvicultural techniques employed to manipulate growth conditions, it becomes difficult for the conservation biologists to propose bat-friendly management measures [2, 81]. The growing literature comparing managed and non-managed forests demonstrates that bats do have the ability to occupy exploited forest systems, which gives hope for improving the conservation status of many species throughout European forests [1]. However, so as to implement effective conservation measures for bats, it is vital to know what habitat parameters to conserve and balance this with appropriate silvicultural treatments that ensure the continuing exploitation of wood while assuring the safety of the loggers themselves and the public who use the forests for recreational purposes. Although it is necessary to further improve knowledge on the relationship between bats and forest management [2], some recommendations can already be put forward. In order to conserve both roosts and foraging habitats, it is imperative that the manager ensures the temporal and spatial continuity of mature broadleaved stands composed of native species by maintaining at least 35% of the surface area of each forest (about 1000 ha). One way of maintaining suitable habitats for bats in forests would be by setting aside a number of small sites of no more than a few hectares in size, leaving the forest within each site to complete its natural cycle. By doing so, this would assure the presence of tree cavities, deadwood, and certain heterogeneity to naturally occur across an entire forest mosaic. In addition, within production forest plots, maintaining a small number of live or dead trees possessing cavities even after felling treatments have been carried out can ensure a minimum continuation of usable roosts. This can be of particular ecological interest: live trees possessing cavities surrounding a dead tree form a group of trees representing a particularly attractive habitat for bats. Also, a tree possessing a large voluminous cavity at a high position can accommodate certain species for an extended period of time such as Nyctalus noctula. Because isolated trees are at a greater risk of falling (due to abiotic factors) it is possible and recommended to maintain a group of trees, ensuring a forest ambience, around a cavity while, again, limiting the potential risk of injury to forestry workers or public. Maintaining quantities of deadwood, where possible both snags and ground-lying, should target the minimal threshold of 25m3/ha. Finally, diversity in tree species, a diversity in the vertical stratification and structure of a forest stand can only further support a diversity and abundance of food resources for the various species of bats.

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7. The involvement of forest managers in France

In Europe, the accumulation of knowledge over the last decade on the relationships between bats and forests has orientated programmes geared towards a greater consideration for bats. In addition, the Natura 2000 network has been adopted in the European Community making it possible to designate numerous sites considered as fundamental for these animals [2, 13]. Forests being a key issue for the conservation of bats need to be taken into account as part of regional planning and forest management policies [2]. However, even though the number of appropriate management recommendations has increased in recent years the implementation of concrete conservation strategies is challenging, and unfortunately slow. Furthermore, forest managers must meet society’s growing demand for wood products among other objectives such as reducing fossil fuel consumption, curtailing the impacts of climate change.

Of the 15 million hectares of forests in France (including overseas territories), 4.5 million hectares are managed by the French Forest Office who are mainly financed by timber production. This management body has integrated key conservation issues for biodiversity at various spatial scales within production forest systems. First, a number of harvest exclusion areas, whereby no silvicultural intervention occurs, have been created, each area ranging in size from ten to hundreds of hectares, totalling nearly 50,000 ha. Second, 3% of managed forests are “habitat islands” (generally ranging from 1 to 10 ha in size) where a true naturalness approach allows the natural cycle of forests to ensue ageing and decomposition of trees. Third, three microhabitat-bearing trees or dead trees are systematically protected per hectare. Fourth, at least one-third of a mature broadleaved forest’s area is maintained in each forest canton as often as possible. The exploitation by clearcutting cannot exceed a few dozen hectares for any single block and the natural regeneration of the ecosystem is favoured, which is thus less degrading to biodiversity than plantations. Lastly, a team of 45 conscientious forest engineers, technicians and ecologists set up in 2004 carry out forest inventories and studies to improve knowledge on the relations between bats and forests and to evaluate the impact of forestry in this Office. They convert the collected information into management guidelines that favour bat conservation. These people are trained in forestry and have years of experience in managing forest plots, and can use the technical terminology required when communicating appropriate strategies to silviculture. The internalisation of these issues by teams dedicated to the preservation of bats within forest management organisations is the best assurance of successful bat conservation within exploited forest systems worldwide.

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Acknowledgments

We would like to reserve a special thanks to the entire Mammal Network Team at the French Forest Office, who have greatly contributed to considering the conservation of bats within the context of forest management in France.

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Written By

Laurent Tillon, Joseph Langridge and Stéphane Aulagnier

Submitted: October 5th, 2017 Reviewed: December 19th, 2017 Published: July 4th, 2018