Volunteer plants obscure the benefits of seed mixes for wild pollinator communities

Creation of new flowering plant habitat is a central approach used to conserve pollinators in degraded landscapes, but the impacts of pollinator‐targeted restoration on forage availability and pollinator communities are surprisingly understudied. We evaluated the abundance and diversity of flowering plants and pollinators (bees + flies) over 2 years on sites that were unmanaged or enrolled in the U.S. Conservation Reserve Program (CRP) for either pollinator‐specific habitat (CP42) or other non‐pollinator conservation goals (i.e. wetland and wildlife). In total, we documented greater than 100 species of flowering plants across all sites with a peak in both abundance and diversity in mid‐summer compared to spring or fall. We also collected 34 genera of pollinators, consisting mostly of bees (25 genera), but also hover flies (8 genera) and bee flies (1 genus). There were no statistical effects of land management type on any plant or pollinator variable. This outcome is likely due to widespread contamination by volunteer plant species (i.e. those that were not intentionally seeded by land managers), which formed the majority of flower observations at most sites. Interestingly, we also found strong significant relationships between seeded plants and all four pollinator variables (sweep/pan × abundance/diversity) but either negative or no relationships when correlating with volunteer plants. These data suggest that pollinator restoration is routinely undermined by poor establishment of targeted plant species. To effectively restore pollinators, more effort needs to be invested in cultivation techniques that reduce habitat contamination by unsown plant species.