Carabid assemblages in agricultural landscapes: impacts of habitat features, landscape context at different spatial scales and farming intensity

Agricultural intensification has led to a major loss of biodiversity, as a consequence of the reduction of permanent landscape elements and the increasing use of inputs. Few studies have considered simultaneously habitat features, landscape pattern and farming systems to explain the changes in biodiversity of agricultural landscapes. This study investigated the respective effects of habitat type, landscape context of habitats and farming intensity on carabid beetles assemblages in hedgerow network landscapes in western France. Carabid beetles were sampled in various permanent landscape elements in three 25 km2 landscape units of contrasting structural complexity and farming systems. The respective importance of habitat type, landscape context and landscape unit were investigated using canonical correspondence analysis (CCA) and partial CCA. The landscape units were the most important variables constraining carabid assemblages (10.3% of variance explained), followed by habitat type (9.3% of variance explained) and, to a lesser extent, by landscape context characteristics (3.9% of variance explained). Large forest species of low mobility were less abundant in landscape units with intensive farming systems and a reduced network of permanent elements. Carabid communities also differed among habitat types, i.e. woodlands and field boundaries. Landscape context characteristics had a low but significant influence on carabid assemblages, forest species being less frequent in landscape contexts with low amounts of woodland and hedgerows. Our results underline the need to consider the relationships between farming systems and landscape pattern for the conservation of carabid diversity in agricultural landscapes. Both the design of suitable habitat at the landscape scale and changes in farming systems should be considered in agri-environmental policies for the conservation of biodiversity in agricultural landscapes.