Pollinator benefits of small‐scale landscapes depend also on semi‐natural habitat

Abstract Farmland pollinators are influenced by landscape structure, including mean field size, floral resources, the amount of semi‐natural habitats and crop type, but their relative importance and interactions for bumblebee colony performance are not well known. In our study, we focused on the concurrent role of crop type (oilseed rape vs. cereal), proximity to semi‐natural habitats (close vs. far) and landscapes with small (average 2 ha) and large fields (average 17 ha) on experimentally exposed bumblebee colony fitness parameters; we also carried out a botanical survey and analysed pollen collected by the bumblebees. We conducted a homing experiment, with workers translocated 0.1–1 km from the colony, and measured the homing speed. We found a significantly higher colony traffic rate next to mass‐flowering oilseed rape fields and close to semi‐natural habitats. According to our structural equation model, higher traffic rates boosted colony growth rates, which in turn supported higher queen brood cell numbers. In the homing experiment, the relocated bumblebees returned to their home colony faster when it was located close to semi‐natural habitats and when the flowering plant species richness was high. The homing speed was lower when semi‐natural habitats were distant and flowering plant species richness was high, possibly due to fewer visual cues. Semi‐natural habitats were more important for pollinators in large‐scale than in small‐scale agriculture. In small‐scale landscapes, bumblebees returned more quickly when flowering plant species richness was low, presumably because the small‐scale landscape structure (higher edge density) allowed for easier navigation by landscape visual cues. The abundance of flowering plants did not affect homing speed, presumably underlining the predominant role of orientation in small‐field landscapes. Synthesis and applications : Mass‐flowering crops and nearby semi‐natural habitats enhance colony growth and queen production, emphasising the important role of abundant and diversified flower resources as well as neighbouring semi‐natural habitats. Further, landscapes shaped by small‐scale farming are crucial for sustaining and enhancing pollinator populations. Our results underscore the need to restore and maintain semi‐natural habitats and to enhance floral resources. These efforts are especially effective in small‐scale agricultural landscapes, which appear to improve bumblebee orientation and support biodiversity‐friendly farming.