Understory vegetation

This chapter documents patterns of species composition and diversity within the understory vegetation layer and provides a species list for the four study areas in southern Ohio. Within each of 108 plots, we recorded the frequency of all vascular plant species in sixteen 2-m² quadrats. We recorded 297 species, including 187 forbs (176 perennials, 9 annuals, 2 biennials), 44 graminoids, 34 shrubs and woody vines, and 32 trees. Only seven species were nonnatives and none of these were abundant. We also documented 12 state-listed species. Detrended correspondence analysis indicated that variation in species composition was primarily along a soil moisture-fertility gradient described by the Integrated Moisture Index. Additional variation in composition among the study areas was correlated with differences in soil texture. Species richness per plot (32-m² sampled) ranged from 23 to 106 and averaged 65.2; richness per quadrat averaged 16.7. All measures of species diversity were significantly higher on mesic than on xeric plots, primarily because forb richness was higher on mesic plots.