Idiosyncratic trends of woodland invertebrate biodiversity in Britain over 45 years

Abstract

Woodland cover in Britain has increased over the past century and is set to increase further through woodland creation schemes aiming to tackle climate change. Nonetheless, the wider repercussions of increasing woodland cover for species, especially invertebrates, have not been comprehensively assessed. Here, we quantified the woodland associations of 2762 invertebrate species in Britain across 21 broad taxon groups using species occurrence records collected by specialist recording societies. We then related the strength of species' woodland associations to published estimates of their long‐term national distribution trends between 1970 and 2015. Across all taxa, 29% of species were positively associated with broadleaf woodland cover, whereas 27% of species were negatively associated. There was a slight tendency for species associated with broadleaf woodland to have more positive long‐term distribution trends, but the effect had little explanatory power. For 15% of species, we detected a non‐monotonic association with broadleaf woodland cover, such that their occurrence peaked at intermediate levels of cover. Intermediate‐cover species had more positive long‐term distribution trends than species with monotonic positive or negative woodland associations. Our findings suggest that woodland invertebrates have not consistently increased, despite the increases in woodland cover. While some caution is warranted owing to our use of heterogeneous occurrence records, the considerable variation in distribution trends of woodland‐associated species could be explained by the high diversity of woodland species and ways in which they use woodland habitat. Woodland creation, or increasing tree cover in general, could have idiosyncratic impacts on species, depending on how new woodlands are created and managed.