Factors associated with plant species richness in a coastal tall-grass prairie

In this study we examine the factors associated with variations in species richness within a remnant tall-grass prairie in order to gain insight into the relative importance of controlling variables. The study area was a smal l, isolated prairie surrounded by wetlands and located within the coastal p rairie region, which occurs along the northwestern Gulf of Mexico coastal p lain. Samples were taken along three transects that spanned the prairie. Pa rameters measured included micro-elevation, soil characteristics, indicatio ns of recent disturbance, above-ground biomass (including litter), light pe netration through the plant canopy, and species richness. Species richness was found to correlate with micro-elevation, certain soil parameters, and L ight penetration through the canopy, but not with above-ground biomass. Str uctural equation analysis was used to assess the direct and indirect effect s of micro-elevation, soil properties, disturbance, and indicators of plant abundance on species richness. The results of this analysis showed that ob served variations in species richness were primarily associated with variat ions in environmental effects (from soil and microtopography) and were larg ely unrelated to variations in measures of plant abundance (biomass and lig ht penetration). These findings suggest that observed variations in species richness in this system primarily resulted from environmental effects on t he species pool. These results fit with a growing body of information that suggests that environmental effects on species richness are of widespread i mportance.