Ecosystematic studies on roadside vegetation in southwestern Virginia
Thirty-two roadside sites throughout seven counties in Southwestern Virginia were investigated with respect to life form, dispersal type and floristics. A floristic checklist of 247 species, 182 genera and 57 families was compiled. Dispersal mechanism and life form were determined for each species. A statistical analysis was performed (ANOVA and MANOVA) to determine the relationships among life form, dispersal type, and environmental factors (roadtype, elevation, exposure, slope and surrounding vegetation). Frequencies of life form and dispersal type were determined within and among sites. These frequencies were used to establish spectra and zonal distributions of life form and dispersal type.
Natural histories, geographic spread and specific modes of dispersal are discussed in the floristic checklist. Family presence among roadtypes and species presence among sites is examined.
Dispersal type variation was found for the environmental factors of roadtype, surrounding vegetation, and exposure. Roadtype was the most influential factor. The dispersal types most subject to variation were the wind (pogonchores and pterochores) and animal dispersed (sarcochore and desmochore) groups. Distribution of dispersal types within the site reveals: 1. Animal dispersal becomes more important when the distance from the road margin is increased; 2. Diaspores that spread by contamination are more frequent near the road margin; 3. Wind dispersed species are less frequent near the road margin.
The life form spectrum of roadsides has a greater percentage of therophyte and lesser percentage of phanerophytes than present in the surrounding vegetation. The spectrum shows infrequent variation (statistically significant) due to the environmental factors considered. Life form frequencies within sites show annuals dominating near the road margin with phanerophytes and chamaephytes becoming more frequent and hemicryptophytes becoming dominant as distance from the road margin increases.