Assessment of the floristic quality index for use in Illinois, USA, wetlands

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The Floristic Quality Index (FQI) is being used in the United States and Canada to assess natural communities. Each native plant species is assigned a coefficient of conservatism, a subjective rating that describes the species' affinity for undisturbed natural areas. To calculate FQI, mean coefficient of conservatism at a site is multiplied by the square root of native species richness. Use of FQI is problematic for several reasons, mainly because FQI incorporates species richness. I assessed FQI based on data gathered between 1992 and 2000 while surveying wetlands in Illinois, USA, for the purpose of jurisdictional determinations. Month of survey affected species richness and FQI even after analysis was restricted to surveys conducted during the growing season. Species number significantly increased with area in all wetland types combined, as well as in floodplain forests, marshes, wet meadows, wet shrublands, and sedge meadows. This significant species-area relationship resulted in a significant increase in FQI with area in all wetland types combined, and in floodplain forests, marshes, wet meadows, and sedge meadows. Furthermore, because the relationship between species number and area varied among community types, the relationship between FQI and area also varied among community types. Specifically, FQI was affected more by area in sedge meadows than in other wetland types investigated. Mean coefficient of conservatism increased with species richness, further increasing the effect of species richness on FQI. Comparisons based on FQI among sites of different community types or among sites surveyed at different times of year may be invalid.

Original languageEnglish (US)
Pages (from-to)53-60
Number of pages8
JournalNatural Areas Journal
Issue number1
StatePublished - Jan 1 2003


  • Floristic Quality Index
  • Sedge meadows
  • Species-area relationships
  • Wetland assessment

ASJC Scopus subject areas

  • Ecology
  • Nature and Landscape Conservation

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