Abstract
Abstract
Pesticides are used around the world to control and suppress undesirable species. In many cases the direct effects of pesticides are well understood and characterized, describing how environments are likely to be altered. However, these direct effects are likely to cause other species to respond to ecosystem alteration. For example, herbicides are applied in forestry to reduce the abundance of competitive vegetation, which could lead to changes in the bumblebee community that rely on flowering plants. We surveyed both the vegetation and bumblebee communities in 35 harvest blocks (4–54 ha in size) that were or were not treated with a herbicide over the last 15 years. Overall, we found the herbicide treatment was associated with differences in plants and bees. General linear models found the abundance of shrubs was lower, while the abundance of forb species and total abundance of bumblebees was higher in herbicide‐treated blocks. Structural equation models (SEMs) demonstrated that herbicide application had a direct negative effect on the abundance and diversity of shrub species and a direct positive effect on the abundance and diversity of forb species. The SEM also detected two indirect effects of herbicides on bumblebees: shrub cover was negatively related to total bumblebee abundance and forb diversity was positively related to bumblebee species richness. Our results suggest that herbicide‐induced changes to the vegetation community lead to changes in the bumblebee community, at least in the short‐term after forest harvesting. As herbicides are applied over large spatial extents in forestry, their use could lead to corresponding changes in vegetation and bumblebee community composition over large spatial areas. Future studies examining more bee species and directly estimating floral resources over different years are needed to generalize the indirect effects of herbicides on bee communities.