Woodland and floral richness boost bumble bee density in cranberry resource pulse landscapes

Abstract

Native pollinators provide an important ecosystem service for many pollination-dependent fruit crops, but require nesting and foraging resources in proximity to target crop plants. Landscape context and fluctuation in floral resources may influence the distribution of pollination services. This study investigates how landscape context influences bumble bee density on cranberry marshes across a resource pulse created by the target crop bloom. We sampled bumble bees at fourteen cranberry marshes before, during, and after the cranberry bloom in central Wisconsin. We quantified floral richness and surrounding land cover and assessed their effects on bumble bee density and colony representation using OLS regression. We measured colony representation as a colony detection rate—where low colony detection means more colonies were represented by single individual foragers. The amount of forest surrounding marshes explained the most variation in colony density, but not colony representation on site. Sites with high meadow interspersion in the surrounding landscape had lower colony representation (i.e., detection rate), suggesting some dilution effect. Colony density and detection did not change between the pre- and post-bloom period and resource pulse, even after statistically controlling for important landscape-scale effects. Yet, relative increase in colony density, was best explained by increased floral richness and decreased open-shrub bog. Landscapes with less clumpy forest experienced increased colony representation during the crop bloom. We suggest maintaining forest within cultivated landscapes to promote local bumble bee colony density, and increasing floral richness on site to attract foraging bees.