Flood-driven survival and growth of dominant C4 grasses helps set their distributions along tallgrass prairie moisture gradients

Five C4 grasses (Bouteloua curtipendula, Schizachyrium scoparium, Andropogon gerardii, Sorghastrum nutans, Spartina pectinata) dominate different portions of a moisture gradient from dry to wet prairies in Wisconsin and other parts of the Upper Midwest. We hypothesized that the distributions of these species may, in part, reflect differences among species in flooding tolerance, and in context-specific growth relative to each other. We tested these ideas with greenhouse flooding and drought experiments, mesocosm experiments conducted under heavy rainfall, and a natural experiment involving graminoid response to a month-long flood in two wet-mesic prairies. Bouteloua appears to be excluded from wet and wet-mesic prairies by physiological intolerance of flooding; it promptly succumbs to inundation in greenhouse and mesocosm experiments. Given its low stature, Bouteloua is likely excluded from more productive, well-drained sites by competition. Schizachyrium is excluded from wet prairies because of its low tolerance to flooding, demonstrated by the natural experiment. Sorghastrum ranked low in flooding tolerance in both the greenhouse and natural experiments, suggesting that physiological intolerance excludes it from wet prairies. Spartina had by far the greatest growth under the wettest conditions in the mesocosms, suggesting that competition helps it dominate wet prairies. Indeed, the quadrat presence of Spartina increased by 57% two years after the flooding of two prairies, while that of upland grasses declined by 44%. Andropogon’s surprisingly high flooding tolerance, its lack of significant difference from other species in drought tolerance, and its tall stature suggest that broad physiological tolerance combined with competitive ability allows it to occur across the prairie moisture gradient.

Methods
See Wernerehl and Givnish 2025, American Journal of Botany for full details.