Searching for Indicator Species of High Floristic Quality Depressional Wetlands in the US Southern Plains

Abstract

Floristic Quality Assessment requires compiling a full list of vascular plant species for the wetland. Practitioners may lack the time and taxonomic skills for full-community vegetation surveys, especially when wetlands are large and complex. In this paper we broadly ask whether floristic quality indicator species may exist for wetlands, specifically evaluating indicator species potential for high floristic quality depressional wetlands in the US southern plains. Candidate indicators were identified for a broader context (depressions across Oklahoma prairie ecoregions) and narrower context (depressions in the northern Central Great Plains of Oklahoma) and evaluated based on performance, validity, and robustness criteria. Nine individual species and two species pairs showed exclusivity and ubiquity for high floristic quality, with their value generally improving in the narrower context. However, the overall best indicator (Eleocharis compressa) frequently occurred (> 20 % rate) in lower quality validation sites, and all indicators were lacking in one or more criteria. Combining E. compressa with select other candidates (Ammannia coccinea, Juncus torreyi, Leersia oryzoides) may compensate for weaknesses of individual species but the combinations may rarely be found across the region, suggesting they may not be useful in practice or that high-quality conditions are in fact scarce. Overall, these results offer mixed support for relying on indicator species to rapidly identify or verify high floristic quality depressional wetlands in the US southern plains. We recommend similar studies with larger datasets in other regions and testing other quality levels (low, moderate) before broadly concluding whether floristic quality indicator species may exist for wetlands.