Pollinator plantings in the intensively farmed Midwest (U.S.A.) support a core set of common bee species, regardless of local and landscape controls

Amidst widespread habitat loss and homogenization of landscapes, pollinator plantings can provide bees with a diversity of foraging resources. Yet, plantings may fall short of restoring historical bee communities. While previous studies have sought to investigate which factors contribute to effective plantings for bee communities, lack of experimental control may have limited their ability to tease apart planting effects versus effects from study design artifacts. We conducted one of the largest randomized, landscape-level experiments to date in order to examine the degree to which planting size, seed mix type (low cost honey bee [HB] mix vs. high cost native bee [NM] mix), and the percentage of natural land surrounding habitat plantings affect native bee diversity, abundance, and composition, in addition to floral abundance, richness, and area. We selected 38 sites for plantings with a fully factorial design, varying sites by seed mix type, size, and proportion of surrounding natural landscape. Despite landscape-level experimental control, bee diversity, abundance, and composition were not significantly related to seed mix type, planting size, or the amount of surrounding natural land. Rather, we found that bee diversity and abundance increased in the first 2 years following implementation and then leveled off. This initial uptick was largely driven by a core set of common bee species from the regional pool. Our findings show that plantings can quickly enhance bee communities; however, there may be limits to the diversity of bees initially supported by these plantings, given the difficulties of establishing diverse plant species on former farmland.