Pacific Northwest native plants and native cultivars part II: plant and pollinator traits.

The use of native plant cultivars in pollinator plantings is somewhat controversial. Although some cultivars originate from wild populations, others are bred for novel ornamental traits, which may have unintended impacts on floral rewards, such as nectar and pollen. It is unclear whether changes in floral displays and/or rewards may alter plant-pollinator relationships. We established an experimental garden of Pacific Northwest native plants and native cultivars to evaluate differences in their floral traits and bee communities. We used a combination of methodologies to quantify variation in plant traits that could influence pollinator foraging, including those associated with floral displays (eg petal color, corolla morphology) and floral rewards (pollen and nectar). We also measured changes in bee community composition (eg species associations, functional diversity) across plant groups. We found that cultivars varied significantly from native plants across multiple floral display or reward traits. No plants were bred for nectar or pollen traits, thus changes in rewards were likely pleiotropic. Nine out of 10 tested cultivars had dissimilar bee communities to their native plant counterpart, though minimally developed cultivars were associated with similar bee species and functional traits. Our results suggest that the development of native plant cultivars can come at the cost of pollinator functional richness, though some variation in bee composition may be expected among wild plant populations with diverse phenotypes. Plants with phenotypes consistent with wild-type plants tended to support functionally rich bee communities and should be emphasized in plantings to maximize potential benefits to pollinators.