Evaluating hedgerows for wild bee conservation in intensively managed agricultural landscapes

Abstract

Wild bees provide essential pollination services to both agricultural crops and wild flowering plant species. The decline of wild bee species has been associated with a number of different threats, primarily the loss of natural habitats. The Delta Farmland & Wildlife Trust (DF&WT), a non-profit conservation organization, incentivizes farmers to plant hedgerows consisting of native shrubs and trees on the edge of their production fields, mainly to create habitat for wildlife in the Agricultural Land Reserve (ALR) of Delta in British Columbia, Canada. In this study, the value of the planted hedgerows was evaluated as foraging habitat for wild bees specifically. During the summers of 2015 and 2016, we surveyed bees and flowers in planted hedgerows, as well as the two other most dominant field margin habitats, remnant hedgerows and grass margins. The relationship between available floral resources and bee abundance and diversity, as well as bee-flower interactions, was analyzed and compared among these three habitat types. Overall, wild bees collected from flowers and pan traps were more abundant, species rich and significantly more diverse in grass margins compared to planted and remnant hedgerows. However, significant results were inconsistent between sampling methods and years, implying none of the habitat types stood out as clearly better. While the strongest relationship was found between floral abundance and bee abundance, it did not explain the differences between habitat types alone. Bee-flower interaction records showed that bees primarily visited herbaceous species mostly found in grass margins while only a few of the recommended woody plant species for hedgerow plantings were visited. The results indicate that grass margins could be a valuable alternative conservation approach or addition to woody hedgerows if properly planned and managed. These results can be used to help improve field edge management for the conservation of wild bee species.