Size, age and surrounding semi-natural habitats modulate the effectiveness of flower-rich agri-environment schemes to promote pollinator visitation in crop fields

Animal pollination is of major importance to wild plants and a wide variety of crops, yet agricultural intensification has led to pollinator declines and yield gaps in agroecosystems. Agri-environment schemes (AES) aim to restore biodiversity and ecosystem services by providing suitable habitats and key resources. Sown flower fields are often implemented as AES and are assumed to partly compensate for the lack of semi-natural habitats (SNH). But the combined effects of local management, size and landscape context on the effectiveness of flower fields remain unclear. We studied five pollinator groups (honey bees, bumble bees, other wild bees, hover flies and other flies) in three types of AES flower fields differing in age, size, and local management along a SNH gradient. We used calcareous grasslands as control sites. Further, we examined distance decay functions of flower visitation rates in adjacent oilseed rape (OSR) fields. Young flower fields in the first year after establishment characterised with high flower cover were very attractive for pollinators, however pollinators tended to remain in these fields when they were large (> 1.5 ha). High amounts of SNH in the surrounding landscape enhanced the value of small flower fields as starting points for pollinators and their subsequent movement into crops. Distance decay of pollinators was reduced in the presence of high amounts of SNH in the surrounding landscape. Based on our results, we recommend establishing smaller sown flower fields in landscapes with high amounts of SNH and larger flower fields in landscapes with low amounts of SNH. Importantly, sown flower fields were no substitute for perennial semi-natural habitats, underpinning the importance of SNH conservation in agricultural landscapes to maintain pollinators visiting flowers in crops.