Comparing the impacts of patch‐burn grazing on vegetation in two northern tallgrass prairies

Abstract The management practice of patch‐burn grazing varies grazing pressure across a site by rotating burn locations, thereby creating spatial heterogeneity in vegetation height and structure. Patch‐burn grazing increases the range of habitats available for different wildlife species, but it may also affect plant invasion and plant biodiversity. We evaluated the effects of patch‐burn grazing on plant communities in two northern tallgrass prairies that were undergoing invasion by the non‐native grass smooth brome ( Bromus inermis Leyss) and had different cattle stocking rates and burning practices (three or five burn units). We established 15–20 plots per site for each treatment of patch‐burn grazing (open) and burning‐without‐grazing (fenced). We measured vegetation structure, native and non‐native plant richness, smooth brome frequency, and frequency‐weighted mean coefficients of conservatism (mean C ) over 5–6 years. At the site with a lower stocking rate and more burn units, grazing promoted spatial heterogeneity by reducing vegetation structure 18%–65% points in some units and some years. In both treatments, native richness increased 15% over 6 years; non‐native richness did not change, but smooth brome frequency increased over 200%. At the site with a higher stocking rate and fewer burn units, grazing reduced vegetation structure 37%–78% points in all units and all years, but native richness was maintained over time. Grazing also increased non‐native richness 38% points but did not change mean C calculated without non‐natives. Smooth brome frequency increased 2% over 2 years in both treatments. We suggest that patch‐burn grazing can achieve structural heterogeneity and sustain native plant species richness in small northern tallgrass prairie remnants; however, higher stocking rates can stimulate the emergence of non‐native species present in the seed bank from past land use, and patch‐burn grazing would not be effective in suppressing the smooth brome invasion that threatens many northern tallgrass prairie remnants.