In tallgrass prairie restoration, dominance by competitive late succession prairie grasses may cause loss of species that are poor competitors. In a field experiment we tested whether disturbance could reverse this process for Liatris scariosa var. nieuwlandii, a threatened savanna species thought to be a poor competitor. At our study site, this species appears to be stable in vegetation dominated by Danthonia spicata, an early successional grass, but declining in the presence of Andropogon gerardii, a dominant prairie grass restored to the study area. We used correlation analysis to test whether cover of grasses affected L. s. nieuwlandii abundance and experimental disturbance to test whether competition could be reduced. We disturbed soil at small (<100 cm2) and large (2.25 m2) scales within vegetation dominated by D. spicata or A. gerardii. We measured the response of L. s. nieuwlandii to disturbance by planting seeds within undisturbed and disturbed patches. In undisturbed patches, cover of D. spicata and A. gerardii was inversely related. Liatris s. nieuwlandii abundance was negatively correlated with A. gerardii cover (R2 = 0.58) but positively correlated with D. spicata cover (R2 = 0.98). In association with D. spicata, L. s. nieuwlanii abundance was significantly lower (<1/0.25 m2) within large scale disturbance plots than in small or no disturbance plots. In association with A. gerardii, L. s. nieuwlandii was absent from undisturbed plots but present (at <1/0.25 m2) in small and large scale disturbance plots. In vegetation dominated by D. spicata, native species richness was greater in undisturbed and small scale disturbance plots than in large scale disturbance plots. Non-native richness tended to be lower in large scale disturbance plots in both vegetation types compaired to small scale or no disturbance plots. The results support the hypotheses that disturbance of dominant grasses can reverse the competitive exclusion of L. s. nieuwlandii by late successional grasses and thus disturbance can mediate the coexistance of early and late successional species.
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