Persistence of Native C4 Grasses under High-Intensity, Short-Duration Summer Bison Grazing in the Eastern Tallgrass Prairie

Abstract

Disturbances such as burning or grazing maintain the herbaceous nature of eastern tallgrass prairie. These disturbances are also known to affect the relative abundance of warm-season (C4) and cool-season (C3) grasses in native prairie. Although burning is a commonly used tool, the utility of livestock grazing to manage restored prairie is less understood. We established five monocultures and one mixture of C4 grass species of the eastern tallgrass prairie in southern Wisconsin. To examine their persistence under high-intensity, short-duration summer grazing, we estimated cover of several functional groups and C4 species over a 6-year period (2000 through 2006) in a randomized complete block design. After a 2-year establishment phase (1998-1999), bison were rotated through paddocks two or three times annually during late June, July, or early August. All C4 grasses declined over time but at different rates depending on the species. Switchgrass (Panicum virgatum) decreased at the lowest rate, whereas Little bluestem (Schizachyrium scoparium) cover declined faster than Big bluestem (Andropogon gerardii), Indiangrass (Sorghastrum nutans), and Sideoats grama (Bouteloua curtipendula), whose rates of decline were not significantly different from each other. Succession followed a predictable trajectory with annual grasses initially colonizing interstitial space among C4 grasses, followed by legumes, which ultimately gave way to exotic C3 forage grasses. The focal C4 grasses remained the dominant functional group 8 years postseeding, but recolonization by non-native C3 grasses increased over the study period.