This study adds to this growing pool of knowledge to suggest that, far from being an “ecological desert” (Brockerhoff et al., 2008), plantations support viable populations of bats, although composition is dominated by two common species (Chapter 2, 5, 7). Both P. pygmaeus and P.
pipistrellus are widespread and common, and although populations have undergone historic declines
(Hutson et al., 2001), there is evidence that populations are beginning to increase (Barlow et al., 2015). Previous studies in the UK have found that bats, including both P. pygmaeus and P.
pipistrellus, often avoid coniferous forest for foraging (Davidson-Watts et al., 2006; Nicholls and
Racey, 2006a; Walsh et al., 1996) and roosting (Bellamy and Altringham, 2015; Boughey et al., 2011; Jenkins et al., 1998), which has been attributed to a low invertebrate diversity and abundance (Walsh et al., 1996). To some extent, this may reflect sampling bias. For example, Boughey et al (2011) used a long-term database of known roost sites which are assessed for occupancy during the summer breeding period and concluded that bats preferentially roost near broadleaf woodland and avoid coniferous forest. However, very few P. pygmaeus and P. pipistrellus roosts assessed as part of their study were in plantation dominated landscapes, although I show in Chapter 6 that substantial roosts of P. pygmaeus do exist near P. sitchensis plantations. This may reflect the lower human population density, and therefore volunteers willing to count roosts in these areas.Furthermore, in studies investigating P. pygmaeus and P. pipistrellus habitat associations, the proportion of
coniferous forest within the landscape is typically very low (e.g. 0.6 - 3.2%, Davidson-Watts et al., 2006), and bats may adjust their behaviour in landscapes with different dominant habitat types. Here, I add to the current understanding of P. pipistrellus and P. pygmaeus habitat associations with riparian and deciduous habitats (Davidson-Watts et al., 2006; Nicholls and Racey, 2006a; Russo and Jones, 2003; Sattler et al., 2007; Walsh et al., 1996), by showing that in plantation dominated landscapes, both P. pygmaeus and P. pipistrellus make widespread use of coniferous plantations. Such differences in responses of bats to coniferous plantations suggests that there is geographical
156
variation in bat habitat associations related to landscape composition (Chapter 2, 6, 7). Bat
associations with commercial plantations, including those consisting of non-native tree species, have been reported from a variety of different regions (e.g. Europe; Charbonnier et al., 2016; Cistrone et al., 2015; Cruz et al., 2016; Mortimer, 2006; Pereira et al., 2016; Russo et al., 2010, New Zealand and Australia; Borkin and Parsons, 2011; Borkin et al., 2011; Burgar et al., 2015 and North America; Morris et al., 2010; Patriquin and Barclay, 2003), emphasising the importance of surveying areas which may appear poor for biodiversity.
Potentially, P. pygmaeus females associate with large, commercial coniferous plantations during pregnancy and lactation due to a high abundance of Culicoides impuctatus (the Highland midge, a highly abundant dipteran species which reaches pest proportions in all three study areas; Marsh, 1986). Bats will adjust their spatiotemporal foraging behaviour in response to invertebrate abundance (Fukui et al., 2006; Gonsalves et al., 2013), and dietary studies have found that P.
pygmaeus and to some extent, P. pipistrellus feed on nematoceran diptera, such as C. impuctatus
(Barlow, 1997). Pipistrellus pygmaeus home ranges recorded during radio tracking were much larger than those reported from other studies (Davidson-Watts et al., 2006; Nicholls and Racey, 2006b; Sattler et al., 2007), with the largest home ranges found in bats roosting furthest from the plantation edge (chapter 6). Bats were flying considerable distances to access plantation areas; one individual regularly flew nearly 40km each night to access preferred foraging areas, suggesting that the abundance of the food supply may outweigh the energetic cost of flight. Furthermore, nights with very high bat activity in both plantation and broadleaf sites were associated with high dipteran abundance (which was almost exclusively C. impuctatus, Appendix 1). Only a small number of bats were tagged, and all were initially captured in plantations, so it is unknown whether the behaviour of these bats reflects behaviour in the wider population. It should be noted however that all but one habitable building (and one uninhabited) within the forest park housed a bat colony, many of them substantial, and it is unlikely that these individuals are commuting long distances out of the
plantation to forage. Tagged individuals that shared a roost were both roosting within plantations and had a high degree of overlap in home range and core area overlap, and usually the smallest home ranges (Chapter 6).
Towards the end of the first tracking season, at the beginning of August, tagged females dispersed out of the plantation area and I was unable to locate them. Pipistrellus pygmaeus is migratory in continental Europe (Fornu, 2009; Sztencel-Jabłonka and Bogdanowicz, 2012), and there is some evidence of migratory movement in the U.K (Racey et al., 2007), although the extent of movement depends on geographical location (Sztencel-Jabłonka and Bogdanowicz, 2012). Migratory movement
157
appears to be modest in the U.K. compared to Central and Northern Europe (Racey et al., 2007; Sztencel-Jabłonka and Bogdanowicz, 2012), possibly reflecting the milder, maritime climate. Very little is known about P. pygmaeus hibernation behaviour, although females are known to join males in harems before hibernation (Park et al., 1996), which may result in some of the population
structuring evident in genetic studies (Sztencel-Jabłonka and Bogdanowicz, 2012). The movement of
P. pygmaeus out of the study area towards the end of summer, coupled with the predominance of
reproductively active female P. pygmaeus, suggests that P. sitchensis dominated commercial
plantations may be an important habitat for P. pygmaeus during an energetically costly period (Kurta et al., 1987), but lack structures necessary for mating or hibernation. This results in the use of plantations during a period coinciding with a reliable and abundant prey source (Fukui et al., 2006; Gonsalves et al., 2013). Picea sitchensis plantations may also be important for p. pipistrellus;
although abundance for this species was low, it may reflect capture bias as activity was equal to that of P. pygmaeus, and the two individuals which were trapped in plantation sites were both
reproductively active females (Chapter 1, 4). Lintott et al (2013) found that relative abundance is correlated with activity for both P. pygmaeus and P. pipistrellus, suggesting that acoustic activity can be used as a surrogate for abundance. If this holds true for commercial plantations, then P.
sitchensis dominated plantations support substantial populations of P. pipistrellus as well as P. pygmaeus bats. Further study is required to understand associations with commercial plantations by P. pipistrellus populations.
Plantation forests also supported a surprising diversity of moth species, with both taxonomic and functional diversity in plantation forests similar to broadleaf sites (Chapter 3, 4). In general, moths associated with deciduous trees have declined throughout Europe, while those associated with conifer have increased due to plantation expansion (Fox et al., 2013; Mattila et al., 2006). The conversion of open heathland to arable and plantations has significantly impacted upon species reliant on open, low nitrogen habitats (Fox et al., 2014). Therefore, while there is a relatively high diversity of moths in plantations, this may be a subset of the former, specialist, heathland and upland community which existed pre-planting. The presence of specialist species in plantations is likely to be due to landscape features and reflect moth dispersal abilities (Scalercio et al., 2012); for example felled and open areas may support early successional specialists, while mature stands may support forest specialist species (Ohsawa and Shimokawa, 2011; Oxbrough et al., 2010). However, the presence of moth species depends on the availability of larval host plants (Franzén and Johannesson, 2007), and that in turn relies on colonisation by suitable plant species, which often come from remnant patches of native habitat (Eycott et al., 2006). Proximity to, and size of the nearest patch of broadleaf tree cover positively influenced both naïve and functional richness
158
(chapter 3, 4), and, although diversity did not differ between broadleaf and plantation sites, functional redundancy was greater in the former. This suggests that remnant patches of broadleaf support rarer species and act as a source, allowing dispersal into other areas of the plantation (Scalercio et al., 2012).
Thirteen biodiversity action plan (BAP) species were identified in plantation sites. BAP species are those which were formally widespread and common but have undergone extremely large declines in the last few decades (70 – 90% reductions, Fox et al., 2013). Eugnorisma glareosa, the autumnal rustic, and Arctia caja, the garden tiger, were fairly abundant in plantation sites (Chapter 3, appendix 4). Climate change, resulting in milder, warmer winters, is detrimental to A. caja, resulting in a northward expansion of its range in the UK (Conrad et al., 2002). Changes in species distribution due to global warming may result in more moth species moving into upland, plantation dominated areas. Increased monitoring within plantation areas will be useful to determine changes in moth species composition and develop sympathetic management practices for moth diversity.