Spatially discrete disturbance processes enhance grassland floral resources

Abstract

Abstract Grasslands provide essential floral resources for both managed and wild pollinators. However, grassland flowers in remaining native landscapes are threatened due to non‐native plant invasions and alterations to historic disturbance regimes such as fire and grazing. The potential for managed disturbance to promote grassland floral resources remains unclear. Fire and grazing historically occurred interactively, but uniform application of each may be a detriment to floral resources and the pollinators depending on them. Though fire can increase resources available to plants and stimulate flowering, it initially destroys floral resources and may delay flower availability. Similarly, grazing removes competitors of flowering plants, but destroys flower heads. To address this knowledge gap, we investigated the impacts of rotational fire and cattle grazing (patch‐burn grazing with one and two seasons of fire per year) versus traditional season‐long grazing with no fire on floral resources in mixed‐grass prairie. In patch‐burn treatments, part of each pasture is burned each year, which focuses grazing activity due to the high‐quality regrowth. We aimed to use fire to remove litter around flowering plants while also sheltering established flower heads from grazing pressure by directing cattle away from regenerating forbs in unburned portions of the landscape. Over two summers, we performed weekly flower surveys in season‐long grazing and patch‐burn grazing pastures. We analysed total seasonal floral resources, maximum floral abundance and seasonal species richness between treatments. Over 2 years, we surveyed 1,238,241 ramets of 160 species, focusing on 36 common species for individual analysis. We found broad positive associations between patch‐burn grazing and total seasonal flower abundance, maximum flower abundance and species richness compared to traditional management. In most cases, patch‐burn grazing with dormant and growing season fires produced higher floral abundance, total seasonal floral resources and species richness than patch‐burning with dormant season fires alone, suggesting benefits of increased levels of pyrodiversity. Synthesis and applications. Under increasing pressure to manage for declining pollinators, rangeland managers must consider strategies to enhance floral resources within the context of livestock production goals. The spatiotemporal interaction of cattle grazing and fire shows promise for promoting floral resource abundance and diversity.