Plant Stewardship Index
Coefficients of Conservatism
Floristic Quality Assessment
The Floristic Quality Assessment Index (FQAI) is a floristic integrity assessment method developed in the Chicago area by Swink and Wilhelm in the 1970’s and 1980’s.
It is based upon two basic ecological tenets:
1) Plants differ in their tolerance to disturbance and disturbance types, and
2) Native plant species exhibit varying degrees of fidelity to habitat integrity.
The FQA methodology is based on a coefficient of conservatism (CC), between 0 – 10, being assigned to each native plant species by a panel of regional experts. Non-native species are assigned a 0 coefficient.
Essentially, a higher coefficient is assigned to those species that are more conservative in their requirements for stable native plant communities. Species with lower CC’s are generally found in a broader range of habitats and are more likely to colonize disturbed ground, abandoned fields, waste ground and old pastures, etc.
Those plants, and plant communities, with exacting habitat requirements score highest, and are also the plants of greatest concern because we are losing them as the landscape is fragmented and developed. The use of an index of conservatism to rank species has been used in a dozen states and has been found to correlate well with wildlife diversity and other environmental indicators.
Assignment of Coefficients
0 to 3 : Plants with a high range of ecological tolerances/found in a variety of plant communities
4 to 6 : Plants with an intermediate range of ecological tolerances/ associated with a specific plant community
7 to 8 : Plants with a poor range of ecological tolerances/associated with advanced successional stage
9 to 10 : Plants with a high degree of fidelity to a narrow range of pristine habitats
How does this relate to the Plant Stewardship Index?
The Plant Stewardship Index (PSI) is a modification of the Floristic Quality Assessment methodology that incorporates the presence and impact of non-native plants on the calculation. The numerical difference between the FQI and the PSI will indicate the impact of non-natives on the site’s quality.
