Herb Distribution in an Acer saccharum Forest

Abstract

Plant distribution patterns in a mesic forest in southern Wisconsin were sampled within a 1.71-hectare area and related to ecologic amplitude, microenvironmental differences and species aut- ecology. Of 30 important herb species, seven were significantly non-homoge- neous. All of the homogeneous species except one were found to have some degree of aggregation (contagion). Herbs as a whole, sampled regardless of species, were randomly distributed and, within clumps, species were distributed in a modified random pattern. An ordination of herbs on the basis of their interspecific association revealed patterns similar to those found in the intermediate to terminal stages of the upland- forest of the region. Seventeen of 41 species were associated with topography, three with the presence of tip-ups, two with drainage channels and one with relatively open areas. Annual species had a higher average seed production and were more homogeneous in distribution than the perennial species which were mainly dependent on vegetative propagation, had a lower seed pro- duction, and were diverse in distribution patterns. in an Acer saccharum forest in southern Wisconsin is presented. These patterns are related to microenvironmental differences within the stand and to ecologic amplitude and some autecological aspects of individual species. Nomenclature throughout the paper is after -Gleason (1952). Grateful appreciation is expressed to Dr. Grant Cottam for aid in all phases of the work and to Dr. J. Roger Bray for reviewing the manuscript. A mesic Acer saccharum forest was chosen for this study since its flora is stable in both time and space compared with other upland forests of the area. An Acer saccharum forest is considered to be the terminal stage of forest succession in southern Wisconsin by Braun (1950) and by Curtis and McIntosh (1951); it is considered to have occupied its present site for several centuries without serious dis- turbance, especially of fire. It is, therefore, hypothesized that the herbs of this forest should have had sufficient time to colonize the entire area and should demonstrate a homogeneous distribution throughout. the stand. Since macroclimate, soil, light, temperature and moisture