Bee Communities and Patterns in Flower Visitation in Crested Wheatgrass Seedings in Eastern Oregon Sagebrush Steppe

Management effects on bee communities, and their relationships with plant communities, are poorly understood in many rangelands such as sagebrush steppe, an ecosystem threatened by broadscale degradation associated with invasive species and other factors. Large areas of sagebrush steppe have been seeded with non-native perennial grasses, such as crested wheatgrass ( Agropyron cristatum ), to bolster forage production and compete with non-native annual grasses. These widespread seedings may influence bee communities, with effects hypothesized to be primarily driven by reductions in floral resources, such as perennial forbs. We investigated the effects of seeding on bee communities by sampling bees with pan traps and netting in paired plots across southeastern Oregon with and without historic crested wheatgrass seedings. We examined the effects of seeding, forb density, and their interaction on bee abundance, richness, diversity, community composition, and bee-plant networks. We found high variability in bee communities associated with site characteristics and sampling methods. Some sites had extremely low perennial forb abundance, and low bee abundance and diversity, in both seeded and unseeded plots. Netting samples suggested decreased bee abundance and species richness with seeding, whereas bee abundance in pan traps was higher in seeded sites. When detected, negative effects of seeding on bee communities were generally greater in sites with higher floral abundance. The relative dominance of some bee traits also varied with seeding, with fewer floral specialists and smaller bees associated with seeding. Although bees and flowering plant interactions were diverse across our study area, interaction patterns were not consistently related to seeding treatment. More research is needed to identify key factors underlying the effects of management approaches like crested wheatgrass seeding on bee communities and to identify key bee-plant interactions for guiding management decisions, such as the composition of restoration seed mixes.