Bee habitat, but not bee community structure, varies across grassland management in four national parks in the Mid-Atlantic, USA
National parks in the U.S. play a large role in providing habitat for native pollinators. In parks that are established to preserve cultural landscapes, park managers recognize an opportunity to improve pollinator habitat while maintaining historically accurate conditions. In this study we document floral resources and native bees within managed park grasslands, with the goal of providing managers information to help them maximize pollinator habitat while meeting other management objectives. The study was performed on 37 grassland properties in the mid-Atlantic region of the eastern U.S., distributed across four national parks; each property was managed with one of three management types: cool-season hayed, cool-season pasture, or warm-season meadows managed with multiple approaches. We surveyed bees and open flowers on 50-m transects twice each year in 2021 and 2022. Repeated measures ANOVA models revealed mean bee abundance, richness, evenness, and diversity did not vary among sites or management types. This finding was further supported by a principal coordinates analysis that showed bee community composition was similar across management types. Nonetheless, we found evidence to indicate the three management types did not produce equivalent habitat for bees. Species accumulation curves showed that the effective number of flower species was consistently lower in cool-season pastures, relative to the other two management types. Furthermore, we detected positive correlations between bee and flower diversity metrics in one of the two years, suggesting that floral metrics can influence bee communities, at least under certain conditions. Collectively, our study suggests that cool-season fields that are hayed and warm-season meadows have higher floral diversity than cool-season pastures within national parks of the mid-Atlantic region, and this higher diversity of forbs has the potential to benefit native bee diversity.