Life History Traits of Exotic and Native Species Determine Grassland Management Outcomes Following Prescribed Fire

Disturbance regimes, including the historical timing of disturbance, are important components of natural ecosystems and greatly influence ecosystem structure and functioning. Consequently, disturbance timing can be an important component of biodiversity management. We evaluated the effect of prescribed fires ignited during the warm and cool seasons (summer and spring, respectively) on the plant community of a calcareous grassland in northern Mississippi (USA). We found that fire season influenced plant community composition by having differential impacts on species with different life history traits. Differences among species were primarily driven by the dichotomy between cool-season (C3) and warm-season (C4) plants, independent of species native status. Spring burns reduced the cover of cool-season C3 graminoids, but had the opposite effect on C4 graminoids, which likely benefited from increases in resource availability due to the reduction of C3 species. However, summer burns decreased the abundance of C4 graminoids, as summer burns were ignited during the active growing and reproductive period for the C4 species. We found the same patterns for the number of inflorescences of the most abundant C3 and C4 graminoids. Summer burns also increased overall species diversity and the abundance of native C3 graminoids, forbs, and vines, resulting in significant differences in plant community composition between spring- and summer-burned areas. Programs that aim to restore native grassland communities in the short-term using prescribed fire should consider the life history traits of target plants (including invasive species) to determine the best time for prescribed fire implementation.