Early Spring Herb Communities in Mesophytic Forests of the Great Lakes Region

Herb composition in early spring (before leafout of hardwood overstories) was sampled quantitatively in 60 little—disturbed mesophytic hardwood stands in the Great Lakes region, USA. Disturbed hardwood stands and stands containing evergreens (hemlock) in the overstory were described by releve. Importance of strictly vernal growth forms, early spring annuals and ephemeroid perennials, was correlated with total cover of herbs. In places with nutrient—poor mineral soil, slow rates of litter decomposition, compressed growing season, or evergreen shade, populations of vernal herbs were generally sprase, with summergreen and semi—evergreen taxa relatively important. In mesophytic woods occupying physiographically similar sites, the most significant regional differences in species importance are associated with differences in soil fertility rather than climate. Superimposed on the soil—related, specific compositional differences were gradual, more general, southeast to northwest decreases in species richness, total cover of herbs, and importance of strictly vernal growth forms (annuals and ephemeroids) relative to herbs with summergreen shoots. Within stand, the most significant influences on vernal herb composition were soil drainage and microtopography. Plants with a large proportion of shoots of recent seed origin (annuals and "weedy" perennials) were often strongly dominant in areas with recently exposed mineral soil, as at the edges of receding vernal pools. Plants with large subterranean organs were rare in such sites. Cover of vernal herbs tended to be high on soil mounds and very low in pits, but differences in species composition were not as well defined as they are in large—area uplands vs. broad poorly drained areas. Species abundant on large patches of bare soil (as at the edges of receding vernal pools) also tended to be common in disturbed stands. Long—lived perennials with large storage organs tended to be uncommon in disturbed stands.