Forests influence pollinator biodiversity and community composition in agroecosystems in Central British Columbia, Canada

Native pollinators provide an important ecosystem service, but pollinator biodiversity may be adversely affected by agricultural practices and climate change. When they are present in agroecosystems, forest fragments may function as refugia for, or net sources of, pollinators for adjacent areas used for crop production. In the Central Interior of British Columbia, we collected pollinator samples at three-week intervals between May and August, 2021, a period that included a record-breaking heat wave. We used UV-painted pan traps, placed near forest edges and in the interior of fields on 15 farms, representing a variety of production systems. Using DNA barcoding (CO1 gene), we identified 72 species of pollinating bee (Hymenoptera) and 63 species of hoverfly (Diptera: Syrphidae) in total. Overall species richness and general diversity indices did not differ between field edges and interiors, but did decline with increased temperatures; these declines were largely due to reduced hoverfly diversity when temperatures rose. Forest edges were associated with greater diversity in leafcutter bees (Hymenoptera: Megachilidae), but pollinator community composition in general differed between field edges and interiors, due to greater abundance of hoverflies, and bees in the families Andrenidae, Colletidae, and Megachilidae, near forests. Field interiors had pollinator communities characterized by greater numbers of sweat bees (Halictidae) and bumblebees (Apidae: Bombus). In this region the retention of forest patches is likely to benefit pollinator biodiversity in nearby agroecosystems, but those benefits are likely specific to pollinators with explicit life-history or resource needs dependent on forests, and those with limited dispersal capacity.