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Agri-environment schemes (AES) were introduced in Europe to mitigate the loss of biodiversity in cultivated landscapes. In Switzerland, farmers have to convert 7% of the arable land into ecological compensation areas (ECA) in order to enhance biodiversity, low-input grassland making up the major part of ECA. This study investigated during 6 years the effect of ECA grassland on butterfly diversity at the field and the landscape scales in two farming landscape units of the Swiss Plateau. Butterfly diversity was compared between low-input and conventional grasslands, controlling for potential influence of local site conditions and landscape context of grasslands. Low-input management of ECA grasslands had a significant impact on butterfly communities, but ECA and conventional grasslands differed more in the composition of species assemblages than in the number of butterfly species. The typical butterfly assemblages on ECA grassland might be linked to the slightly higher plant species richness due to management restrictions. However, the effectiveness of ECA grassland for promoting butterfly diversity varied according to local site conditions (field slope and orientation) and to the amount of ECA and semi-natural elements in the surrounding landscape. Thus, the present study underlines the necessity to account for such environmental variation at multiple scales to be able to detect and interpret effects of AES. Nevertheless, our results suggest that additional restoration measures should be adopted. Especially, the ECA scheme should promote a connected network of ECA grasslands and semi-natural habitats at the landscape scale.
