Spatiotemporal patterns of forest pollinator diversity across the southeastern United States

Efforts to understand how pollinating insect diversity is distributed across large geographic areas are rare despite the importance of such work for conserving regional diversity. We sampled bees (Hymenoptera: Apoidea), hover flies (Diptera: Syrphidae), and butterflies (Lepidoptera) on nineteen National Forests across the southeastern U.S. and related their diversity to ecoregion, landscape context, canopy openness, and forest composition. Bee richness was negatively correlated with both the amount of conifer forest and the extent of wetlands in the surrounding landscape but was positively correlated with canopy openness. Hover flies and butterflies were less sensitive to landscape context and stand conditions. Pollinator communities differed considerably among ecoregions, with those of the Central Appalachian and Coastal Plain ecoregions being particularly distinct. Bee richness and abundance peaked two months earlier in Central Appalachia than in the Coastal Plain and Southeastern Mixed Forest ecoregions. Our findings suggest that hardwood forests may play a particularly important role in supporting forest-associated bees in the southeastern U.S. and that efforts to create more open forest conditions may benefit this fauna.