Wild bee community recovery in restored grassland-wetland complexes of prairie North America

Abstract

Agricultural intensification is a widespread driver of global pollinator decline that subsequently threatens the associated provisioning of ecosystem services. In North America's Prairie Pothole Region, wetlands surrounded by grassland were once abundant on the landscape, but now generally exist within a matrix of agriculture. We assessed whether restoration of these grassland-wetland complexes from cropland could be used as a potential tool for mitigating wild bee decline, using a 25-year restoration chronosequence. We also monitored the development of bee nesting and food resources to better establish the mechanisms that drive return to a restored habitat. Our objective was to assess whether restoration of grassland-wetland complexes can return bee communities to a reference state (i.e. remnant native grassland-wetland habitats), and to ascertain the timeline over which these changes occur. We found bee diversity increased following restoration and approximated reference sites after 1–4 years, while the diversity of non-Bombus species analyzed separately resembled reference sites after around 5–10 years. Floral diversity also increased following restoration from cropland but remained slightly lower than reference sites through time. Changes to bee species composition were driven more by floral species composition than time since restoration. Our results suggest that restored grassland-wetland complexes are able to provide food and nesting resources to bees within agriculturally dominated landscapes, and that restoration can recover wild bee communities to a reference state. On a broader scale, they underscore the utility of retaining patches of non-cropped and restored land within agroecosystems as a pathway for mitigating pollinator decline.