Using Floristic Quality Index to evaluate success of restorations

At the Grassland Research Network meeting today I learned that a number of prairie restoration projects in various states are using the Floristic Quality Index value as a measure of the success of a restoration. To calculate FQI, one needs to know the number and name of all the species in a prairie, and the Coefficient of Conservatism (C) of each.

The C value is given to each native species on a state-wide basis. Each species is assigned a value from 0 to 10, that represents the probability that this plant species is likely to occur in landscapes relatively unaltered from those of presettlement times. Plant species with relatively specialized requirements are given higher C values, reflecting the fact that they are found in more restricted habitats.

The FQI is then calculated by multiplying the average C for the site by the square root of the number of species present at that site. According to some researchers, an FQI greater than 50 represents an area of high conservatism and an area with an FQI greater than 35 is considered floristically important in the state.

The FQI value for Pleasant Valley Conservancy as a whole unit was found to be 91.5.

The concepts of FQI and C were created by Swink and Wilhelm, from the Morton Arboretum in Chicago, and can be found in their widely used book: "Plants of the Chicago Region." Details of C and FQI for Pleasant Valley Conservancy can be found elsewhere in this web site.

Frankly, I can see considerable limitations in FQI. It may have value in comparing successes of restorations in a local area, but comparing FQIs across distant geographic areas is probably inadvisable. Among other things, the assignment of a C value to each species is a subjective exercise.

However, FQI might be used to justify restoration work on a particular prairie remnant. Those of low FQI may be so degraded as to be too costly to restore, whereas those with higher values might be worth investing time and money. However, experienced restorationists might be able to make such a decision simply by walking a site.