Floristic Quality Assessment (FQA)

The Army Corps of Engineers has made available a pdf document explaining how FQA’s are produced and used. The following paragraphs are excerpts from that document describing the FQA and its primary feature, the Coefficient of Conservatism. See also U. of Wisconsin explanation and the book by Swink and Wilhelm. 1994. Plants of the Chicago Region (4th Ed.)

Floristic Quality Assessment (FQA)

FQA is a standardized method for natural area assessment utilized by a number of national and local government agencies. This method replaces the subjective measures of quality, such as “high” or “low,” with an objective quantitative index. FQA methods were developed to quantify the biological integrity of a site based on the condition of the plant community. The basis for an FQA is the concept of species conservatism. The method uses the aggregate conservatism of all species found on a site as an indication of its ecological integrity.

Coefficient of Conservatism

The Coefficient of Conservatism is the main component of the FQA (Herman et al. 2001; Rothrock 2004; and Rocchio 2007). This coefficient, also known as the “C of C” value, or merely the “C” value, is an integer ranging from 0 to 10 (Rocchio 2007). Species given low C values are highly tolerant to disturbance, and, in fact, may actually thrive upon disturbance (Rothrock 2004). These particular species exhibit little fidelity to natural areas and may be found virtually anywhere (Rocchio 2007). As an example, Swink and Wilhelm (1994) noted that common peppergrass (Lepidium virginicum) found in the Chicago region would be assigned a C value of 0, representing 0% confidence that the species was from a natural community. In contrast, species with high C values are highly intolerant to disturbance and are located in high quality natural sites indicative of conditions prior to European settlement (Rocchio 2007). An example in this case could be rush aster (Aster borealis); if found in the Chicago region, it would be assigned a C value of 10 (Swink and Wilhelm 1994). This C value represents 100% confidence that this particular species was from a natural community. Since physiological and ecological differences may exist within the growing range of a plant, different C values for the species are likely, depending upon the specific geographic region (Rooney and Rogers 2002; Rocchio 2007; Robert W. Freckmann Herbarium website, http://wisplants.uwsp.edu/WFQA.html). In these cases, a species found near the periphery of its growing range is likely to have a higher C value compared to that which it has in the central part of its range (Rooney and Rogers 2002; Rocchio 2007; and Robert W. Freckmann Herbarium website).