Análisis de los Resultados de las Encuestas

Clear felling was the only management technique commonly carried out across all the study sites, reflecting current forestry practices in Picea sitchensis dominated plantations in the UK (Andrew Jarrott, pers.comm). Similar to studies in native managed forest systems, activity increased post felling for some species (Dodd et al., 2012; Grindal and Brigham, 1998; Loeb and O’Keefe, 2011; Patriquin and Barclay, 2003; Pauli et al., 2015). Nyctalus spp. and to some extent P. pipistrellus and

P. pygmaeus activity increased in felled compared to control stands, particularly where the area of

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at felled stands compared to other stand types for both P. pipistrellus and Nyctalus spp (chapter 2). It is likely that increased activity reflects selection of these areas for foraging (Appendix 1; Dodd et al., 2012). Based on wing morphology, the increase in Nyctalus activity was expected, as both species in this genus in the UK are fast, high flying, open adapted bats (Aldridge and Rautenbach, 1987). Both P. pygmaeus and P. pipistrellus are edge adapted bats, increased activity may reflect their ability to exploit forest edges created by clear felling which allow easier flight and prey capture (Dodd et al., 2012). It is likely that bats are responding to reduced physical and acoustic clutter rather than increased invertebrate abundance (Dodd et al., 2012; Jung et al., 2012; Titchenell et al., 2011), especially as I found no difference in non-Lepidoptera invertebrate abundance between different stand types (appendix 2.4). Furthermore, felled patches were positively selected by the majority of radio-tracked bats at the local level, suggesting that bats move between felled patches to forage on accessible and reliable dipteran populations (chapter 6).

Activity of both P. pygmaeus and P. pipistrellus was lower with larger areas of recently felled stands (chapter 5), similar to findings from other studies (Law and Law, 2011; Patriquin and Barclay, 2003). Although Grindal and Brigham (1991) found no effect of the size of the cut block on bat activity, it is likely that the felled patches in their study were too small to detect any differences (0.5 – 1.5ha). In contrast, in this study, where the size of felled areas reflects common forestry practice, cut blocks were far larger (2.9 – 39ha). Overall bat activity was higher at stand edges rather than stand interiors, regardless of stand type (chapter 2). Higher activity in smaller felled areas is likely due to the increased provision of edge habitats which are structurally simple compared to forest interior (Hogberg et al., 2013; Jung et al., 2012), provide shelter from predators (Grindal and Brigham, 1998), and may harbour a larger invertebrate prey population due to microclimatic variables (Baker et al., 2013; Verboom and Spoelstra, 1999). Larger stands have proportionally less edge compared to interior than smaller stands, and may be more exposed to predation risk and adverse microclimatic effects (Baker et al., 2013).

Knowledge of how bats respond to felling practices is important in understand the potential implications of siting wind turbines in plantations, a practice which has greatly increased in recent years. There is overwhelming evidence to suggest that wind turbines cause both direct and indirect mortality through barotrauma, collision, and avoidance resulting in changes to habitat use (Voigt and Kingston, 2015), although the extent to which such effects can exert population level impacts is likely to vary greatly between regions. Current practices involve the felling the area in which turbines are to be installed, and then replanting up to around 50m beyond the turbine blade tip (Anon., 2015), a process known as keyholing. This may create a patchwork of attractive foraging patches within which turbines have been installed, acting as an ecological trap (Tscharntke et al., 2012). Since it is

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assumed that bat activity in upland plantations is low, there are currently no requirements for monitoring post felling and post construction and no guidance on the potential impacts on bats (Mathews et al., 2016). Results from this thesis suggest that some bat species could be at far greater risk from the installation wind turbines in commercial plantations than previously thought.

In line with other studies, all species responded negatively to stand density, with decreased activity or a reduced probability of recording certain species as stand density increased (Bender et al., 2015; Blakey et al., 2016; Cistrone et al., 2015; Cox et al., 2016; A D Morris et al., 2010). Again, this is likely to reflect the increased structural, and therefore physical and acoustic clutter in dense stands (Jung and Kalko, 2010; Patriquin and Barclay, 2003). Thinning is not common in the study areas examined in the thesis, and even in mature stands, the average stand density was 1250 trees ha-1_.

Recommendations of thinning to below 1100 trees ha-1 _{(Adams et al., 2009) are likely to be effective,}

Blakey et al (2016) found increased bat activity in stands which were thinned to below this level, and in this study bat activity increased by 30% in stands in which density was below 1000 trees ha-1

(Chapter 2).

As a result of forest restructuring, U.K. forest guidelines now require a proportion of the plantation landscape to be broadleaf tree cover and surviving remnant patches of broadleaf trees are protected from forestry practices (Pommerening and Murphy, 2004). Preserving broadleaf patches in the environment is likely to benefit bat species by alternative roost provision (Altringham et al., 1996) or due to increased invertebrate diversity (Felton et al., 2010; van Halder et al., 2008). Of the two Pipistrellus species recorded in this study, P. pygmaeus was more common close to broadleaf woodland. Since the majority of broadleaf woodland was within 200m of a building, and most of these buildings contained a P. pygmaeus roost (Appendix 1, chapter 6), associations with broadleaf woodland in our study area are therefore conflated with the locations of roost. However, the presence of deciduous trees in commercial coniferous plantations has been linked with increased bat activity (Charbonnier et al., 2016), and as lactating female P. pygmaeus did use deciduous trees as both night and day roosts, preserving them in the plantation landscape is likely to benefit bats, particularly tree roosting dependent species. Although dipteran abundance was not significantly greater in native stands within the plantations (appendix 2.4), preserving broadleaf woodland is likely to support a greater diversity of invertebrate species.