Invasive plants are a leading cause of ecological change in natural areas. However, control of invasive plants may also have negative effects. For example, removal of invasive plants could have conflicting impacts on pollinator and flowering communities. Exotic plants can provide food and nesting resources for native bee species. In contrast, exotic, invasive plant species can negatively influence native plant communities which are the natural food sources for native bees. In forest systems, flowering plants provide a critical early-season resource. Land managers have struggled to remove the ornamental landscaping plants, Common or European buckthorn (Rhamnus cathartica) and Glossy buckthorn (Frangula alnus). The goal of this study is to determine bee use of buckthorn and use of native plants that co-flower with buckthorn. In collaboration with the Exotic Plant Management Team of the National Park Service (NPS) as part of the Great Lakes-Northern Forest Cooperative Ecosystem Studies Unit (CESU). Teams identified areas of concern for invasive species management and native bee sampling. In 2017 and 2018, we characterized bee and flowering plant communities in forested areas of the Saint Croix National Scenic Riverway and Mississippi National River and Recreation Area. Bee specimens were collected while visiting buckthorn and other ephemeral flowers.
Results/Conclusions
Over the course of two field seasons, 1147 individuals were collected and identified to genus (2017 = 614; 2018 = 533). The number of individuals captured on buckthorn were similar between years (2017 = 21; 2018 = 30) and constitute only 4% of individuals captured. Genera caught on buckthorn included mostly generalist foraging groups (i.e Andrena, Apis, Augochlorella, Ceratina, Lasioglossum, Halictus, Dialictus). According to this 2 year data set, buckthorn pollen and nectar resources make up very little of forest pollinator foraging activity. Other forest plants frequently visited by forest pollinators include Erythronium albidum, Geranium maculatum, Glechoma hederacea, Claytonia virginica, Prunus americana, Sambucus racemosa, and Sanguinaria canadensis. These ephemeral plants represent the bulk of forest pollinator use. This information is useful to land managers and invasive species eradication teams because it demonstrates that invasive buckthorn is infrequently visited by bees and thus buckthorn removal may have little impact on forest pollinators. Our data on other floral associations could help target particular forest flowering plants to focus on for bee conservation efforts.