Beyond Floristic Quality: A Data-Driven Approach to Assessing Coastal Wetland Condition Using Plants.

Plant communities are commonly used to assess ecological condition due to their sensitivity to local environmental factors and the practicality of conducting vegetation surveys. Using a large dataset (41,314 survey plots from 563 wetlands across 12 years), we developed and tested a new plant-based Index of Biotic Condition (pIBC) for coastal wetlands for each of the five Laurentian Great Lakes. The pIBC shares conceptual similarities with Floristic Quality Assessment (FQA) metrics but incorporates species-specific sensitivity and responsiveness to anthropogenic disturbance based on modeled probabilities of occurrence derived from field data. This distinguishes it from traditional FQA metrics, which rely on expert-assigned Coefficients of Conservatism and do not incorporate occurrence probability. We found that each lake-specific version of the pIBC consistently predicted anthropogenic disturbance, as indicated by water quality and surrounding land use. Additionally, comparisons with seven other plant-based metrics showed that the pIBC generally provides greater within-lake sensitivity to water-quality and land-use impacts, providing higher-resolution insight into spatial and temporal variation at the lake scale, which is often the most relevant scale for management decisions. The pIBC was also applicable across wetlands of different hydrogeomorphic types and under different water-level conditions. The pIBC's strong performance suggests that it is well-suited for assessing coastal wetland condition across sites and within sites through time. Overall, this new index is a conceptually grounded and statistically robust tool for conservation practitioners that is easy to calculate and interpret. Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s13157-026-02094-z.