A plant-based index of biological integrity (IBI) for headwater wetlands in central Pennsylvania

Vascular plants are quickly emerging as one of the best indicators of human-mediated disturbances in the environment. We developed a plant-based index of biological integrity (IBI) to evaluate headwater wetland condition in response to anthropogenic disturbances in the Ridge and Valley Physiographic Province of central Pennsylvania. To construct the IBI, we evaluated 50 attributes of the plant community, including species richness, diversity, and evenness. Disturbance was quantified for each site using information on surrounding land use, buffer characteristics, and an assessment of potential site stressors. Ecological dose–response curves were then plotted to evaluate the relationship between each attribute and the disturbance score. Eight attributes showed a consistent and strong response to disturbance and were selected as metrics: adjusted FQAI, % cover of tolerant plant species, % annual species, % non-native species, % invasive species, % trees, % vascular cryptogams, and % cover of Phalaris arundinacea. All metrics were highly and significantly correlated (P < 0.001) with disturbance as were IBI scores. To test the IBI, we used data from 47 sites collected as part of the Juniata Wetland Monitoring Project. The metrics and IBI scores for this data set were also significantly correlated with disturbance. Although, to date, very few plant-based IBIs are in use, studies from Minnesota, Massachusetts, and Ohio, as well as our study in Pennsylvania demonstrate the efficacy of plant community measures in assessing the overall condition of wetlands.