Is the effect of farming practices on songbird communities landscape dependent? A case study of olive groves in southern Spain

Abstract

Extensive farming practices and landscape heterogeneity promote biodiversity in agroecosystems. However, the effect of such practices might be landscape dependent; specifically, the effect might be greatest where the loss of heterogeneity has been the largest. In recent decades, agricultural intensification and landscape simplification have dramatically affected the Mediterranean region, where olive groves are one of the predominant crops. For instance, in Spain from 1996 to 2008, the amount of land dedicated to olive groves increased by 300,000 ha (12 %). In conventional olive farming, herbicides are applied intensively to minimize competition between crops and swards for water; however, to prevent erosion, many farmers are maintaining swards within crops. This practice likely benefits farmland biodiversity, although the heterogeneity of the surrounding landscape might influence the extent of these effects. This study assessed the effects of herbaceous cover on the abundance and species richness of songbird communities in six matched pairs of olive groves (ground cover or bare ground) in homogeneous and heterogeneous landscapes over a 3-year period. We predicted that (1) the presence of ground cover and landscape heterogeneity would have a positive effect on songbird communities, and (2) the effect would be greatest in homogeneous environments. Although bird community composition differed among landscape types and farming practices in the olive groves in southern Spain, the effect of ground cover was not landscape dependent. The presence of ground cover had a positive effect on the abundance and richness of songbirds, including sensitive species, but landscape heterogeneity did not have an effect. This study underscores the important role of agricultural practices in preserving farmland bird communities, while it also suggests that landscape heterogeneity might not be very important in Mediterranean perennial farming systems. The positive effects of ground cover can be important for preserving the wintering quarters of numerous European bird species, including species of conservation concern.