Limited Evidence For Indicator Species of High Floristic Quality 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 wetlands in the US southern plains region. Indicators were identified for a broader context (wetlands in Oklahoma prairie ecoregions) and narrower context (depressional wetlands in the northern Central Great Plains ecoregion of Oklahoma) based on indicator value, indicator validity, hydrophytic status, and ecological conservatism. No candidate indicators satisfied all criteria for high floristic quality. Indicator values improved with increasing spatial-environmental context, but many candidates occurred too frequently in non-high quality sites or too infrequently in high quality sites, relative to predicted rates. The best performing indicator (Eleocharis compressa) lacked validity in the broader context and showed high false-positive rates in the narrower context. Combining E. compressa with select other candidates (Amorpha fruticosa, Juncus torreyi, Leersia oryzoides, Schoenoplectus pungens) may compensate for weaknesses but the combinations may rarely be found across the region. Overall, these results do not support relying on indicator species to rapidly identify or verify high floristic quality wetlands in the US southern plains. We recommend similar studies in other regions and testing other quality levels (low, moderate) before broadly concluding that floristic quality indicator species do not exist for wetlands.