Environmental Correlates of Herb Species Composition in Five Southern Wisconsin Floodplain Forests

The hypothesis that variations in major environmental factors can explain herbaceous species composition in floodplains is examined by multivariate analyses of five southern Wisconsin floodplain forests. Species composition within sites varied with relative elevation: Carex and annual forbs dominated lower elevations, whereas perennials dominated higher areas. Elevation within sites had a higher correlation with major ordination axes than did light or soil variables. However, light and soil texture were correlated with herb distribution independently of elevation. Compositional change with elevation was gradual; no discontinuities were discovered. Quadrats under canopy gaps and at higher elevations supported more species than closed canopy areas. Sites most recently flooded during the growing season were species-poor, with vegetation patterns summarized relatively well by a single ordination axis. Thus, compositional differences between sites could be due largely to effects of recent floods.