No evidence of decline in bumblebee abundance and species richness from edge to interior in moderately-sized red clover fields

Mass-flowering crops have the potential to mitigate the negative effects of agricultural intensification on resource availability for pollinators, but their full utility also depends on pollinators providing consistent pollination services across the entire field. However, the spatial extent of pollination services in mass-flowering fields remains poorly understood, particularly within the landscape context. We evaluated bumblebee abundance and species richness along the gradient from field edge to center in mass-flowering red clover fields, while also accounting for the composition of the surrounding landscape and field size. Additionally, we examined within-field foraging patterns of individual bumblebee species. Bumblebee species richness and abundance were assessed during peak flowering in 27 clover fields in Estonia, along transects extending from field edge to field center at equal distances. Nearly all true bumblebee species (20 of 21) of the national fauna were observed to forage on red clover fields. Contrary to our expectations, bumblebee foraging patterns in the studied fields did not show a negative edge-to-center gradient. While species richness did not change within fields, abundance even tended to increase toward the field interior. The responses of individual species varied, ranging from no edge-to-center change (Bombus lucorum, B. terrestris) to a decline (B. pascuorum). Neither field size nor the composition of surrounding landscape influenced the observed foraging patterns. The absence of edge-to-center trends in bumblebee species richness and abundance cautiously suggests that pollination services may be relatively evenly distributed in moderately sized mass-flowering fields within a diverse landscape. Consequently, field size is unlikely to be a major limiting factor for effective pollination in this system.