Potential Vegetation Criteria for Identifying Reference-Quality Wetlands in the South-Central United States

Reference criteria are needed for wetland monitoring and assessment programs. We used field-collected vegetation data from non-forested wetland sites in the south-central United States to establish preliminary criteria for identifying reference-quality wetlands in future surveys. Our analysis included three parts: (1) preliminary reference verification and metric ranking using boxplots and standardized effect size, (2) updating the putative reference sample and metric selection using Test Site Analysis, and (3) establishing reference criteria from best-metric confidence intervals and indicator species combinations. The Floristic Quality Assessment Index most clearly distinguished the reference wetlands; an index value of at least 20 is recommended for future reference designations in the study region. Other potential reference criteria include a maximum of 3–5 % bare ground in the 100 m buffer, a moderately sensitive species assemblage (mean conservatism > 5.0), a small percentage (<10 %) of tolerant species (coefficient of conservatism ≤ 2), and high native richness (>22 species). Five single species, four pairs, and one triplet combination were extracted as potential indicators of reference sites from 70,375 combinations of 75 candidate species, offering an efficient alternative to sampling entire vegetation communities. The analysis framework in this case study could be useful for similar projects in other regions.