1. Agricultural expansion and intensification have resulted in strong declines in farmland biodiversity across Europe. In many intensively farmed landscapes, linear landscape elements such as field boundaries, road verges and ditch banks are the main remaining green infrastructures providing refuge for biodiversity, and as such play a pivotal role in agri-environmental policies aiming at mitigating biodiversity loss. Yet, while we have a fairly good understanding of how agricultural intensification influences biodiversity on farmland, little is known about whether and how local land-use intensity affects biodiversity in nearby linear landscape elements and how this affects their role as biodiversity refuge.

2. Focussing on pollinating insects, we examined the effects of local land-use intensity on biodiversity in agricultural fields and adjacent green infrastructures. In an intensively farmed area in South-Western France, we selected 23 agricultural grasslands and nearby field boundaries along a gradient in grassland cutting frequency which acted as a proxy for land-use intensity. We analysed how grassland cutting frequency affects species richness, abundance and community composition of wild bees and hoverflies in the grasslands and neighbouring field boundaries, and whether these effects differ across habitat types and species groups.

3. Grassland cutting frequency negatively affected pollinator species richness and abundance in the grasslands, whereas pollinators in the neighbouring field boundaries were unaffected. These responses reflected the effects of cutting frequency on floral resources, with flower cover and richness decreasing in grasslands but not in field boundaries. As a result, the proportion of the local pollinator community supported by field boundaries increased with the increasing cutting frequency of the adjacent grassland.

4. Common and rare pollinator species generally showed similar responses. Furthermore, communities of plants and pollinators in field boundaries next to intensively farmed grasslands were fairly similar to those next to extensively farmed ones.

5. Synthesis and applications. Our results suggest that, as nearby land-use intensifies, flower-rich field boundaries become increasingly important as pollinator refuge habitats. Conserving field boundaries and other green infrastructures, and maintaining or enhancing their quality, therefore constitute important tools to conserve and promote pollinators in intensively farmed landscapes.

Data was collected in the Long Term Socio-economic and Ecosystem Research Platform Zone Atelier “Plaine & Val de Sèvre” in south-western France. We surveyed wild bees, hoverflies and flowers twenty-three sites, each consisting of a grassland and a nearby field boundary. The survey was conducted in four separate rounds from June to August in 2015 using standardized transect walks. Data on cutting frequency of grasslands in 2015 was collected through interviews conducted with farmers in early 2016. Arable land cover and semi-natural habitat cover in 2015 within radii of 500 m and 1 km of each grassland-field boundary pair was calculated based on yearly land-use monitoring at the field scale over the study area.

Species richness and abundance data of pollinators and flowers were aggregated over the two transects per habitat at each site. We classified wild bee and hoverfly species into rare and common species according to their proportional abundance in this study. Species accounting for less than 1.0% of the total number of individuals were classified as rare species, the other species were considered as common species.

We calculated Bray-Curtis community similarity index of wild bees, hoverflies and flowers based on abundance data of each species in each habitat per site (aggregated over the two transects and four rounds). The reference grassland was randomly selected from those with the lowest cutting frequency (once a year). The field boundary adjacent this reference grassland was considered as the reference field boundary. We calculated similarity indexes for three comparisons: (a) between each field boundary and the reference field boundary; (b) between each grassland and the reference grassland; (c) between each grassland and its adjacent field boundary.

Only the pollinator individuals identified to species level were included in classifying species classes (common and rare species) and calculating similarity indexes. Two sites were not included when we calculated similarity indexes because they were surveyed less than four rounds.