Effects of ecological compensation meadows on arthropod diversity in adjacent intensively managed grassland

An important goal of ecological compensation areas (ECAs) is to increase biodiversity in adjacent intensively managed farmland and the agricultural landscape at large. We tested whether this goal can be achieved in the case of the agri-environmental restoration scheme implemented for Swiss grassland using five large arthropod taxa (bees, true bugs, orthopterans, ground beetles and spiders) representing different ecological and functional groups. The species richness and abundance of all groups and species, respectively, was measured along 100 m transects from ECA-meadows into the adjacent intensively managed grassland at 24 sites. Species richness of all arthropod taxa except ground beetles, and the abundance of 63% of the 234 arthropod species sampled with at least five individuals were higher in ECA-meadows than in their surroundings, while the total abundance of spiders and ground beetles was higher in intensively managed meadows. The abundance of 8% of these species were only increased in the ECA-meadows themselves (“stenotopic” species) but 40% had increased abundance both in the ECA-meadows and the adjacent grassland, declining exponentially with increasing distance from ECA-meadows (“edge species”). The 90%-decay distances for these edge species differed among taxonomic groups (117 ± 18 m for true bugs, 137 ± 24 m for spiders, 152 ± 34 m for bees, 167 ± 5.7 m for orthopterans, 185 ± 34 m for ground beetles; mean ±1 standard error) and independent of taxonomic group were larger for large-sized or predacious species than for small-sized or phytophagous species. Because the average distance between neighbouring ECA-meadows in Swiss grassland is only 73 ± 4 m, the current agri-environment scheme very likely enhances arthropod diversity and possibly associated ecosystem services in the Swiss agricultural landscape at large.