Determinants of overwintering habitat quality for beetles and spiders on arable farmland

The provision of overwintering refuges has important implications for both conservation of invertebrate biodiversity on farmland and biological control of crop pests. In this study we carried out a systematic investigation of the effects of habitat type and age on the quality of overwintering refuges for Coleoptera and Araneae on an arable farm in the UK. Hedgerow habitats contained taller and more diverse vegetation with a greater proportion of bare ground compared with field margins. Vegetation height and diversity, and the richness and cover of forbs all increased significantly with habitat age. Soil organic matter content also increased with habitat age, suggesting a more favourable structure for burrowing Coleoptera. Total abundance and richness of Coleoptera and Araneae were significantly higher in hedgerow habitats compared with the field margins. This largely reflected the response of staphylinid beetles, the most abundant group recorded. There was no effect of habitat age on overall abundance or diversity, suggesting the good dispersal ability of many farmland invertebrates, but also reflecting the close relationship between habitat age and type. The response of individual invertebrate species was more mixed: 10 species were recorded in significantly higher densities in the hedge base compared with one in the field margin. Similarly, eight species were recorded in significantly higher densities in mature habitats compared with four in recently established vegetation. There were significant interactions between habitat type and age for six species, of which four showed a marked preference for the base of mature hedgerows. These included both important predators of cereal aphids and crop pests. It was concluded that hedgerows provided the highest quality overwintering habitat for invertebrates emphasising the importance of strategies directed at conserving and enhancing this habitat. However, newly created field margins fulfilled a useful role in rapidly providing overwintering refuges for a more limited group of invertebrate species.