Macrophyte species distribution, indices of biotic integrity, and sampling intensity in isolated Florida marshes

Abstract

This study examined the distribution of wetland plants used in macrophyte-based index of biotic integrity (IBI) metrics to determine the effectiveness of zone sampling in assessing wetland condition. Using sampling data from a previous study of 74 emergent isolated wetlands, macrophyte taxonomic data and resulting IBI metrics were analyzed for various wetland zones and compared against the original site metrics. Zones were defined by parsing each sampling transect (from wetland edge to center) into thirds—creating an outer, intermediate, and inner zone—and constructing two additional zones representing two-thirds of the original sampling area—an outer plus intermediate zone and an intermediate plus inner zone. While a highly-significant decrease in mean species richness was observed from the wetland exterior to interior, there were no significant differences between metric values derived from site data and those derived from zone data. Linear correlations between metrics from the outer zone and site data were highly significant (R2>0.94), but linear correlation strength decreased with the intermediate and inner zones, respectively. Thus, macrophyte-based indicators of biological integrity can be efficiently assessed by sampling the outer third of a wetland—a 66% reduction in the area and effort required to monitor isolated wetland condition.