Landscape diversity and field border density enhance carabid diversity in adjacent grasslands and cereal fields

Abstract

Permanent grasslands have declined across Europe since the agricultural intensification. Grassland vicinity, landscape heterogeneity and vicinity of hedgerows are enhancing factors for farmland carabid (ground beetle) diversity. However, interrelation between grassland and cropland communities needs to be better known in various landscape context. In this study we disentangle the effects of different landscape indicators carabid communities of adjacent grasslands and cereal fields to assess mutual benefits of these two land cover types. We sampled carabids in three agricultural plains of southeastern France, each associated with a gradient in grassland coverage. We used regression models to point out effects of landscape indicators on the separate, overall and common carabid species richness of paired cereal crops and grasslands. Landscape Shannon diversity and field border density explained best gamma species richness. In grasslands, we found a higher species richness when the landscape diversity increased, except in the study region dominated by grasslands. In cereal crops, the landscape parameters showed no significant effect on carabid richness. Finally, the common species richness from cereal fields and grasslands was explained by higher density of field borders between them, but also by higher grassland coverage where grasslands were the scarcest. Our results suggest that cropland carabid communities may benefit from the habitat and resource complementation provided by grasslands. This finding pleads for the preservation of grasslands in cropped landscapes to favor carabids and illustrates the potential for enhanced biological control in future cropping systems with reduced pesticide inputs.