Landscape context of organic and conventional farms: Influences on carabid beetle diversity

Carabid species richness and density were studied in 12 pairs of organic versus conventional wheat fields located along a gradient of landscape complexity (quantified as percent cover of grassland, which was correlated with habitat-type diversity). The relative impact of local and landscape features was analyzed by comparing sites with similar landscape context but different management systems using pitfall traps. Organic and conventional management did not differ with respect to species richness and activity density. Seven species were more abundant under organic management, and eight species were more abundant under conventional management. The effect of landscape complexity was independent of management system. Species richness increased with percent cover of grassland in the surrounding landscape, and activity density followed the same trend. Hence, surrounding grassland appeared to act as a major source of diversity for farmland carabids. In particular, the activity density of spring breeders on organic fields benefited from the increased availability of overwintering habitats in their close surrounding. It was concluded that landscape features were much more important than organic farming management for enhancement of local biodiversity and should thus be considered in agri-environment schemes.