Local-scale attributes determine the suitability of woodland creation sites for Diptera

Abstract

New native woodlands are typically created in a small and isolated configuration, potentially reducing their value as a resource for biodiversity. The use of ecological networks for habitat restoration and creation could be beneficial for woodland biodiversity. This approach is conceptualised as local and landscape-scale conservation actions to increase the area, quality, amount and connectivity of habitat types. However, there is limited evidence about the value of secondary woodlands and the relative or combined effects of network variables for woodland insects.  Seventy-eight woodland sites created in the last 160 years across England and Scotland were sampled for hoverflies (Diptera: Syrphidae) and craneflies (Diptera: Tipuloidea), using two Malaise net traps placed in the centre of each woodland. The diversity of insects supported by created woodland patches was analysed using measures of dissimilarity, and the relative direct and indirect effects of ecological network variables on their abundance and species richness were assessed using structural equation models.  We found 27% of British woodland hoverfly species and 43% of British woodland cranefly species in the study sites, indicating that woodland insects are colonising created native woodlands, despite their fragmented nature. However, these species communities were highly variable across woodland patches.  Landscape-scale variables had no effect on woodland-associated hoverflies or craneflies relative to local-scale variables. Local-scale variables relating to habitat 34 quality (i.e. structural heterogeneity of trees and understory cover) had the strongest influence on abundance and species richness.  Synthesis and applications – To benefit woodland-associated Diptera, woodland creation and restoration should maintain a focus on habitat quality. This should include active management to facilitate a diverse tree and understorey vegetation structure. Many woodlands in the UK are privately owned and landowners should be encouraged to plant and actively manage their woodlands to increase structural heterogeneity and resources for woodland insects.