Wild bees provide essential pollination service to both agricultural crops and wild flowering species. The decline of wild bee species has been associated with a number of different threats, primarily the loss of natural habitat. The Delta Farmland & Wildlife Trust (DF&WT), a non-profit conservation organization, incentivizes farmers to plant hedgerows on the edge of their production fields, mainly to create habitat for wildlife. To date, it is not known whether these plantings enhance wild bee communities specifically. During the summers of 2015 and 2016 we investigated whether field margins planted with native shrubs and trees in the Agricultural Land Reserve in Delta, British Columbia increased wild bee abundance, species richness, diversity and floral resources, in comparison to two common, unmanaged field margin types: remnant hedgerows and grass margins. Vegetation was surveyed visually and bees (wild and honey bees) were sampled with either aerial nets or pan traps. The relationship between floral resources and wild bees found in each field margin type was then analyzed to evaluate the value of planted hedgerows for wild bees. This analysis was used to update the list of suitable floral plant species for the DF&WT hedgerow restoration program.
Results/Conclusions
Wild bees passively collected in pan traps were significantly more abundant, species-rich and diverse in grass margins than in planted and remnant hedgerows in both years. Abundance and species richness of wild bees collected with nets was significantly higher for grass margins in 2015 as well, but no difference between field margin types was found in 2016. Grass margins had the highest floral abundance in 2015 and a significantly higher floral species richness compared to both hedgerow sites, whereas in 2016 planted hedgerows were found to have a higher abundance and species richness. A weak, but significant positive relationship for floral abundance and netted bee abundance and species richness was found, however only when including honey bees, due to their high proportion in netted bee samples (52.6 %). Ten out of the 16 visited floral species by wild bees were weedy species and only four of the 16 were recommended for hedgerow restoration by the DF&WT. These results indicate that floral abundance or floral species richness alone are not sufficient indicators for wild bee communities, but that plant species selection must be chosen properly to target wild bees. Grass margins could be a valuable alternative conservation approach or addition to hedgerows if properly planned and managed.