A Potential Understory Flora for Oak Savanna in Iowa

Oak savanna occurred in Iowa until the time of settlement and then was degraded rapidly. There were no scientific studies of savanna prior to, or after, settlement, and now no high-quality examples exist within the state. To identify those vascular plants adapted to live in the understory of savanna we examined regional and local flora for species that occurred in both prairie and broken woodland, and for species that occurred m both openings and forest. We then compiled a detailed description of the ecological range of habitats for each of these species. We identified 252 species (39 graminoids, 183 forbs, 5 vines, 25 shrubs and small trees) as potential inhabitants of the understory of day-loam savanna; 150 of these species were found commonly or frequently across the state. We also identified 35 additional species as potential inhabitants of the understory of sand savannas. Of the 52 families represented, Asteraceae included 22% of all species; Poaceae, 13%; Fabaceae, 9%; Rosaceae 7%; and Scrophulariaceae, 5%. Common to frequent forb species were widely distributed in the upper Midwest: 83% occurred in savannas in at least one other state, 44% occurred in two states, and 16% occurred in three states. Although the range of habitats of only 8% of the species included both prairie and closed-canopy woodland, most of these species occurred in a broad range of plant communities, soil moisture levels and soil types