Are native and non-native pollinator friendly plants equally valuable for native wild bee communities?

Bees rely on floral pollen and nectar for food. Therefore, pollinator
friendly plantings are often used to enrich habitats in bee conservation
efforts. As part of these plantings, non-native plants may provide
valuable floral resources, but their effects on native bee communities
have not been assessed in direct comparison with native pollinator
friendly plantings. In this study, we performed a common garden experiment
by seeding mixes of 20 native and 20 non-native pollinator friendly plant
species at separate neighboring plots at three sites in Maryland, USA, and
recorded flower visitors for two years. A total of 3744 bees (120 species)
were collected. Bee abundance and species richness was either similar
across plant types (mid-season and for abundance also late season) or
lower at native than at non-native plots (early season and for richness
also late season). The overall bee community composition differed
significantly between native and non-native plots, with 11 and 23 bee
species found exclusively at one plot type or the other, respectively.
Additionally, some species were more abundant at native plant plots, while
others were more abundant at non-natives. Native plants hosted
more specialized plant-bee visitation networks than non-native plants.
Three species out of the five most abundant bee species were more
specialized when foraging on native plants than on non-native plants.
Overall, visitation networks were more specialized in the early season
than in late seasons. Our findings suggest that non-native plants can
benefit native pollinators, but may alter foraging patterns, bee community
assemblage, and bee-plant network structures.