Restoring Heterogeneity-Based Management to Rangelands for the Benefit of Grassland Birds and Floral Resources

Abstract

Worldwide grassland loss necessitates careful consideration of management practices occurring on those grasslands that remain. Concerns with overgrazing in the early twentieth century led to overcorrection via uniform, moderate stocking. While these practices reversed some forms of rangeland degradation, they also suppressed variability in vegetation structure that is characteristic of native systems. Reduced heterogeneity resulted in biodiversity declines across many trophic levels. In an effort to restore heterogeneity, we reinstated the historic processes of fire and ungulate grazing. We studied the impacts to grassland birds and floral resources, as the Northern Plains are valuable landscapes for breeding grassland birds and both native and managed pollinators. We conducted our research at the Central Grasslands Research Extension Center in Streeter, North Dakota, USA. From 2017-2020, we evaluated grassland bird community composition, nest survival, and floral resource availability. We found that patch-burn and season-long grazing pastures had higher avian diversity than modified twice-over rotational grazing. Avian community composition was also sensitive to ecological site, topographic variability, and wetland area, suggesting that both the fire-grazing interaction and underlying inherent topoedaphic variability maintain biodiversity. Species densities were sensitive to different sources of heterogeneity, with some responding to inherent landscape conditions and some responding to imposed grazing management. We found no differences in nest survival between grazing treatments for any of our 12 focal species despite treatment differences in vegetation and structural components associated with survival. Survival of five species was associated with vegetation structure, and one was associated with litter depth, smooth brome, and forb cover, respectively. We found higher nesting densities of three species (Chestnut-collared longspur, Northern pintail, Brewer’s blackbird) in patch-burn pastures compared to season-long pastures. All are associated with shorter, sparse vegetation. At a treatment scale, we found that patch-burn grazed pastures had shallower litter, less smooth brome, more forbs, and shorter vegetation structure than season-long pastures. Patch-burn grazing pastures increased floral resources across the majority of species. Patch-burn pastures had higher species richness, seasonal availability, and maximum abundance compared to season-long grazing. Our results broadly show the benefits of heterogeneity-based management on two important grassland guilds, birds and flowering plants.