Prior to Euro-American settlement of the Oak Openings in northwestern Ohio, the proportion of oak savanna, woodland and forest in upland sites likely varied, with open canopies developing during dry periods of higher fire frequency and denser canopies developing during wet periods of lower fire frequency. Wet prairie and oak barrens, which persisted in the landscape because of spring flooding, likely contained savanna species and, therefore, may have been sources of propagules of savanna species that colonized areas of newly opened canopy. We used regression analysis to test the hypothesis that the richness and diversity of savanna species in the herb layer of present-day savanna are related to the proximity of former wet prairie and oak barrens. Results were statistically significant for richness but generally not for diversity. This suggests that wet prairie and oak barrens may have acted as refugia and therefore as sources of propagules for savanna species during temporal shifts in the proportions of oak savanna, woodland and forest, but relative species abundances likely were determined more by local environment.