Professor Iowa State University Ames, Iowa, United States
Abstract: Tallgrass prairie contains plant species that flower sequentially throughout the growing season, and this extended flowering is the goal of many pollinator restoration projects. However, it is poorly known what ecological factors lead to extended flowering. Here, we test the hypotheses that extended flowering is due to having: 1) species that flower early and late in the growing season present, 2) a greater number of forb species in a seed mix, 3) management that mimics top-down disturbance, and 4) an intermediate grass/forb (GF) ratio in a seed mix. We tested hypotheses 1-3 in an experiment that added early and late-flowering forb species at different richness levels, comparing additions with mowing to those without mowing in an ongoing restoration. We tested hypothesis 4 by seeding a restoration with different GF ratios at restoration onset. Flowers were counted either monthly (forb addition experiment) or weekly (GF experiment) from the beginning to the end of the growing season, and flowering niche breadth calculated the evenness of flowering across time periods within a year. In the forb addition experiment, there was a marginally significant effect of adding early and late-flowering forbs on flowering niche breadth (p = 0.06). Flowering niche breadth increased linearly with the number of early and late-flowering forb species added (p = 0.01). Mowing promoted greater flowering niche breadth compared to not mowing (p < 0.05). Also, it was revealed that adding early and late-flowering forbs as transplants resulted in greater flowering niche breadth compared to adding them as seeds (p < 0.05). In the GF experiment, plots with intermediate GF ratios had significantly greater flowering niche breadth (quadratic, p = 0.05). Taken together, our results indicate that flowering can be extended in tallgrass prairie with additions of a larger number of early and late flowering species and by including a seed mix with high functional diversity with an intermediate mixture of grasses and forbs.
