Sinus management: meandering mowing as a novel method to improve pollinator biodiversity and habitat heterogeneity in mesic grasslands

Abstract

The decline of European grassland biodiversity underscores the urgent need for innovative methods to address this crisis. Adequate management is essential to reverse this trend while there remain important knowledge gaps addressing effective implementation. This study investigated a novel mowing method, sinus management, compared to conventional block mowing, in extensively managed mesic grasslands. Sinus management employs curved, meandering mowing lines instead of straight ones, resulting in a three times greater mowing length, while the mown:unmown area is kept fixed at 2:1. In addition, a key feature is the retention of unmown edges in various stages of plant (re)growth, while the central area is mown as usual. This approach aims to enhance spatio-temporal habitat heterogeneity, to support diverse pollinator communities by providing proximate and varied food and shelter resources over the full season. We showed that, after already two years, and confirmed in the third year, sinus mowing had a significant effect on bee and butterfly diversity indices. Specifically, there was a positive effect on different functional groups of bees (polygolectic bees with different nesting behavior and cleptoparasitic bees) and butterflies (grassland specialists). Sinus management also fostered more unique plant-pollinator relationships compared to block mowing. The strong positive response on pollinator diversity underscores the potential of sinus management as a sustainable, nature-based management solution to enhance habitat quality of extensively used grasslands, while controlling for excessive succession. This also aims to better conserve essential ecosystem services at risk, notably the pollination of wild plants and crops. Within an agricultural landscape context, a targeted improved grassland management supporting diverse pollinator assemblages, even at local sites, has the potential to effectively link ecological conservation measures with tangible economic benefits for farmers and land managers.