EU tree density limits in wooded pastures and their effects on bat populations within traditional agricultural landscapes

Abstract: The European Union’s Common Agricultural Policy (CAP) recommends subsidies are only granted for wooded pastures with less than 100 trees per hectare. This arbitrary guidance exists despite these habitats being among the most biodiverse in rural Europe. To date, most biodiversity research in agricultural landscapes has focused on plants, birds and invertebrates. Bats are also important bio-indicators of agricultural landscapes, but to my knowledge no study has explicitly focused on bat diversity in relation to this policy. In this thesis, I investigate how bat activity, foraging and species richness is affected in twenty-six wooded pastures along a gradient of tree density, from open to dense pastures. In parallel, nearby open fields and deciduous woodlands were sampled, creating a triplet of habitats being surveyed simultaneously. Bat species were divided into feeding guilds to explore how functional diversity affects response to habitat and landscape configuration. The overall contribution of wooded pastures to the species pool of bats within a heterogeneous, low intensity agricultural landscape was also explored. I found a consistent increase in bat activity and species richness within wooded pastures along the tree density gradient and across most feeding guilds. This in combination with shrub density was the strongest predictor of total bat activity and foraging; whilst structural diversity of pastures was most strongly correlated with species richness. Wooded pastures contributed more to total species richness than forested habitats. Interestingly, higher activity levels of forest feeding specialists were observed in pastures compared to forests. At the landscape level, amount of water and deciduous forest were the strongest predictors of bat activity. This study demonstrates that tree density within wooded pastures is not a limiting factor of bat activity and that other habitat and landscape parameters are important. Wooded pastures may also be an important component of current landscapes with little remaining deciduous forest. In conclusion, focusing solely on tree density limits will not help to preserve the ecological requirements for bats within agricultural landscapes.