Landscape context and carabid beetles (Coleoptera: Carabidae) communities of hedgerows in western France

Dramatic changes have occurred in agricultural landscapes of western Europe since the 1950s. Their effects on biodiversity have been documented at local scales in terms of agricultural practices and management of uncultivated elements, more than at the landscape level. The highest diversity of agricultural landscape structure found in Brittany (France) is characterised by hedgerows surrounding arable fields and permanent grasslands. Some areas did not change much over a few decades, while others were totally transformed by agricultural intensification, field enlargement and removal of hedges. The present paper aimed at examining if this landscape context affected carabid beetles communities in hedgerows. In 11 sites of 1 km^2 each, land use diversity and heterogeneity, hedgerow connectivity and landscape openness were measured. Carabid beetles sampled in hedgerows were identified to species, and grouped in functional units. Multivariate analyses were used to relate the spatial distribution of insects to different parameters of landscape structure. The results show a significant relationship between landscape structure and carabid communities. Forest species were more abundant in dense hedgerow networks with a relatively high ratio of permanent grasslands. Landscape opening induced a shift in species composition; the relative abundance of large species decreased while small, mobile and more ubiquitous species were favoured. Two trajectories of landscape change were identified, which led to different responses in communities, the increase in maize for milk production opening the landscape far more than cereal crops associated with industrial pig or poultry production. Changes were most important in the latter case.