Effectiveness of the Swiss agri-environment scheme in promoting biodiversity.
Increasing concern over the loss of biodiversity in agricultural landscapes was one of the reasons for the introduction of agri-environment schemes in Europe. These schemes compensate farmers financially for any loss of income associated with measures aimed to benefit biodiversity. Nevertheless, more than a decade after the introduction of the schemes, only a limited number of studies evaluating their ecological effects have been published. We assessed the effect of the Swiss agri-environment scheme that was designed to maintain and increase species richness in hay meadows. In Switzerland, hay meadows under this agri-environment scheme (ECA hay meadows) are the most widely adopted environmental measure to conserve biodiversity. We tested whether meadows under the agri-environment scheme had higher species richness and species evenness than control meadows, whether species richness and species evenness were higher in the centre than at the edge of meadows, and whether these effects differed between geographical regions. Biodiversity was sampled in 42 hay meadows in three different regions, using a pair-wise comparison of ECA hay meadows with conventionally managed hay meadows. Biodiversity was estimated by assessing species richness and species evenness of four taxonomic groups representing different trophic levels: vascular plants, grasshoppers, wild bees and spiders. Species richness of vascular plants, grasshoppers and wild bees was significantly higher on ECA hay meadows than on control meadows, but species richness of spiders did not differ. These results were consistent across the three study sites, except for the species richness of grasshoppers, which showed no difference between the ECA meadows and the control meadows in one region. Species evenness was significantly higher on ECA hay meadows than on control meadows for plants and bees but not for spiders and grasshoppers. These results were consistent across the three study regions for bees and spider species only. The species richness of vascular plants and spiders was higher at the edge than in the centre of both ECA and control meadows, suggesting a more extensive management in the meadow edges and a high species exchange between adjacent habitats for these two groups. Synthesis and applications. We conclude that the Swiss agri-environment scheme for hay meadows positively affects biodiversity. The scheme should be maintained and farmers should be encouraged to engage in long-term extensive management. For spiders, the current management restrictions are not sufficient, most probably because of inappropriate vegetation structure. Therefore, organisms that particularly depend on vegetation structure should be targeted with additional restrictions: not only the time of the first cut but also the frequency of subsequent cuts and the mowing technique may have to be adjusted.