Management strategies may alter flowering phenology and/or the availability of floral resources, with important implications for pollinators and plant reproductive success. Recent efforts to return natural fire-grazing regimes to rangelands have focused on the effects of heterogeneous burning regimes on biodiversity and productivity. Heterogeneous burning regimes interact with selective foraging by livestock to increase the structure and diversity of plant communities, including the abundance and diversity of forbs. However, little is known about how fire and fire/grazing interactions effect flowering phenology and floral resource availability. We evaluated the effect of burn season (spring and summer) and time since burn (year of burn and one year after burn) on flowering phenology and nectar availability for several species of flowering forbs commonly visited by bees at managed rangeland sites in north-central Oklahoma. We recorded plant morphological measurements, phenological stage, nectar volume, and nectar concentration.
Results/Conclusions
Flowering phenology did not vary with season of and time since burn for Hedyotis nigricans. Flowering phenology varied with time since burn, but not season of burn for Psoralea tenuiflora and Asclepias viridis, with more individual plants in a vegetative state and flowering phenology shifted later during the year of burn. Plant height was shorter during the year of burn for all species, but other morphological characteristics varied by species and treatment. Reproductive effort was greater with spring burns than summer burns for H. nigricans, but was greater with summer burns than spring burns for P. tenuiflora. Reproductive effort was greater with more time since burn for A. viridis, but did not differ with season of burn. Nectar availability varied among species and treatments. The results of this study suggest that burning regimes may alter flowering phenology and the availability of floral resources. These floral responses will influence the responses of pollinators to these management strategies, with important implications for the availability of pollination services at larger spatial scales.