Robert W. Freckmann Herbarium


Plants of Wisconsin

Vascular Plants

Wisconsin Floristic Quality Assessment (WFQA)

WFQA- Method
Floristic Quality Assessment
Floristic quality assessment is a standardized tool that can be used for natural area assessment, including site assessment of wetland floristic quality and for long-term site monitoring.  Originally developed by Floyd Swink and Gerould Wilhelm, the method can replace very subjective measures of quality, such as “high” or “low”, with a still somewhat subjective, but more dispassionate, quantitative and uniform set of measures.  These measures allow for comparison of the floristic quality among many sites and for tracking changes at the same site over time. The Wisconsin Floristic Quality Assessment allows the application of the method to Wisconsin plant communities on sites anywhere in the state.  It is not intended to be used as a stand-alone method, but rather to complement and corroborate other methods of evaluating the natural quality of a site.  Swink and Wilhelm in Plants of the Chicago Region (1994) provide a thorough discussion of the rationale behind the floristic quality assessment method.

Site Conservatism and the Floristic Quality Index
The FQA method is based on calculating an “average coefficient of conservatism” and a “floristic quality index” for a site.

The method uses a predetermined Coefficient of Conservatism (C), that has been assigned to each native plant species in Wisconsin, based on that species’ tolerance for disturbance and fidelity to a particular pre-settlement plant community type. Because they were not involved in the pre-settlement landscape non-native plants are not assigned conservatism coefficients. There are also several unranked native species whose value is at this time unassigned.The aggregate conservatism of all the plants inhabiting a site determines its floristic quality. Once a thorough site inventory of the vascular plants has been conducted the method calculates a mean C value (meanC), and a floristic quality index (FQI).

The mean C value for a given site is the arithmetic mean of the coefficients of all native vascular plant species occurring on the entire site, without regard to dominance or frequency. Non-native species are not considered in the calculation of mean C or FQI.

The Floristic Quality Index is the mean C times the square root of the total number of native species (sqrtN) inventoried on the site (FQI = meanCsqrtN). This formula combines the conservatism of the species present with a measure of the species richness of the site.  By multiplying by sqrtN, instead of N, the formula reduces the effect of the size of the site (larger sites tend to have a larger total number of species present). If the sampling method involves transects and quadrats a mean C and FQI can be calculated for each quadrat and transect.

The Use of  FQA as an Assessment Method
Higher mean C and FQI numbers for a site indicate higher floristic quality and biological integrity and a lower level of disturbance impacts.  However floristic quality assessment should be recognized as only one indicator of biological integrity and should not be used as the only method if a thorough assessment of a range of attributes is required. Wildlife habitat, presence of rare and endangered species, hydrologic and landscape functions, and human uses will also need to be assessed to thoroughly evaluate a site. The validity of the method is also dependent on the completeness and accuracy of the vegetation inventory. Use of Floristic Quality Assessment, especially in regulatory situations, is limited by these considerations.

Coefficient of Conservatism:
Definition of Coefficient of Conservatism
A number on a scale from 0 to 10 that represents an estimated probability that a plant species is likely to occur in a landscape relatively unaltered from what is believed to be a pre-settlement condition. A C of 0 indicates the probability is almost 0, while a C of 10 indicates the plant is almost certain to be found only in an undegraded natural community.  Introduced plants were not part of the pre-settlement flora, so no coefficient is assigned to them.  Coefficients were also generally not assigned to varieties, hybrids and subspecies. There are also several unranked native species whose value is at this time unassigned.

The Concept of Species Conservatism
The concept of species conservatism is the foundation of floristic quality assessment. Each native species is assigned a coefficient of conservatism (C) following the methods described by Swink and Wilhelm (1994) and Wilhelm and Masters (1995). Coefficients of conservatism range from 0 to 10 and represent an estimated probability that a plant is likely to occur in a landscape relatively unaltered from what is believed to be a pre-settlement condition. Introduced plants were not part of the pre-settlement flora, so no coefficients are assigned to them.

Numerical values assigned to a particular species are based on the observed behavior of populations within a defined geographic area, in this case the state of Wisconsin.  For example, a C of 0, is given to plants such as Acer negundo, box elder, that have demonstrated little fidelity to any remnant natural community, i.e. may be found almost anywhere. Similarly, a C of 10 is applied to plants like Calypso bulbosa, calypso orchid, that are almost always restricted to remnant cedar swamps, i.e. a high quality natural area. Plants that reliably occur in native communities but occur on both degraded and undegraded sites are given an intermediate value, such as Tradescantia ohiensis, common spiderwort, which is assigned a value of 5 in Wisconsin.

The conceptual difference between a value of 0 and a value of 1, or between 9 and 10, is slight, while the difference between a value of 0 and a value of 3 is more distinct. Certain species are known to exhibit varying degrees of conservatism over their range. This creates difficulties when values must be assigned considering as a single region so large and variable an area as the entire state of Wisconsin. For example, Abies balsamea, Balsam fir, is restricted to fewer habitats and would justify a higher C in southern Wisconsin. In northern Wisconsin this same species may be found over a broader range of natural communities and even disturbed sites, so it would justify a lower C. In this case an intermediate C value of 5 was assigned. Concerns over any particular C value are usually compensated within the floristic quality assessment method since it computes the average C value of all the native species that occur at a site.

How Were the Wisconsin Coefficients Assigned?
Wisconsin has a wealth of botanical expertise to draw on. For this project twelve botanists and field ecologists from a list of over 30 responded to a survey and submitted preliminary coefficients for the species they knew well. The final coefficient values were assigned by consensus of six botanists, utilizing the survey results, but ultimately basing the assignments on their collective experience with the flora of Wisconsin. They were aided by Gerould Wilhelm who facilitated the face-to-face group meetings. The six participants in the “core group” were:

Theodore Cochrane
Gary Fewless
Robert Freckmann
Richard Henderson
Emmet Judziewicz
Lawrence Leitner

The assignments are subjective, but it is the collective subjectivity of experts. For aquatic plants the coefficients assigned previously by a group of aquatic ecologists led by Stanley Nichols were accepted (Nichols 1998) with only a handful of adjustments.

Numerical values assigned to a particular species are based on the observed behavior of populations within Wisconsin. As one travels away from Wisconsin these values may become less valid. The further away one goes the more likely these values do not reflect local conditions.

Coming Soon – WFQA Computer Program and Reporting Page
FQA values (mean C and FQI) for a site must be considered in relation to other sites within the same region. As this method becomes more widely used and the range of FQA values for a given region becomes known, future site values will be more meaningful. In order to develop a database of site values across the state, we encourage users of the WFQA methodology to share their results with us and the Wisconsin DNR via a reporting page that will be developed for this website.
A computer program to apply the Wisconsin Floristic Quality Assessment method is currently under development by the Wisconsin DNR. A reporting page for collecting WFQA results is also being developed. These will both be accessible from the WIS-DNR's website in the future.

For more information:

Wisconsin Floristic Quality Assessment Project:
Contact Tom Bernthal, Wetland Ecologist, Department of Natural Resources
Phone: 608-266-3033

FQA computer programs for areas outside Wisconsin:
As of October 2001, Floristic Quality Assessment computer programs for the Chicago Region, Illinois, Michigan, Iowa, Kentucky and the Dakotas are available from:

Conservation Design Forum
375 W. First Street
Elmhurst, IL  60126
Tel. (630) 559-2000

Future FQA databases will likely include Indiana, southern Ontario, northeastern Ohio, and Missouri.

Unranked Natvie Species:These species have not been assigned a coefficient of conservatism at this time.
Barbarea orthoceras Ledeb.
Crataegus acutiserrata Kruschke
Crataegus anomala Sarg.
Crataegus beata Sarg.
Crataegus coccinioides Ashe
Crataegus desueta Sarg.
Crataegus distincta Kruschke
Crataegus douglasii Lindl.
Crataegus holmesiana Ashe
Crataegus irrasa Sarg.
Crataegus margaretta Ashe
Crataegus nitidula Sarg.
Crataegus prona Sarg.
Dennstaedtia punctilobula (Michx.) T.Moore
Eleocharis tenuis (Willd.)Schult. var. verrucosa (Svenson)Svenson
Rubus ablatus L.H.Bailey
Rubus adirondackensis L.H.Bailey
Rubus alumnus L.H.Bailey
Rubus baileyanus Britton
Rubus curtipes L.H.Bailey
Rubus dissensus L.H.Bailey
Rubus elegantulus Blanch.
Rubus exsularis L.H.Bailey
Rubus ferrofluvius H.A.Davis,A.M.Fuller & T.Davis
Rubus fulleri L.H.Bailey
Rubus glandicaulis Blanch.
Rubus groutianus Blanch.
Rubus ithacanus L.H.Bailey
Rubus junceus Blanch.
Rubus meracus L.H.Bailey
Rubus miscix L.H.Bailey
Rubus missouricus L.H.Bailey
Rubus multifer L.H.Bailey
Rubus multiformis Blanch.
Rubus perspicuus L.H.Bailey
Rubus plicatifolius Blanch.
Rubus plus L.H.Bailey
Rubus recurvans Blanch.
Rubus regionalis L.H.Bailey
Rubus rosa L.H.Bailey
Rubus satis L.H.Bailey
Rubus semisetosus Blanch.
Rubus spectatus L.H.Bailey
Rubus steelei L.H.Bailey
Rubus stipulatus L.H.Bailey
Rubus superioris L.H.Bailey
Rubus uniformis L.H.Bailey
Rubus uvidus L.H.Bailey
Rubus vagus L.H.Bailey
Rubus vermontanus Blanch.
Rubus wheeleri (L.H.Bailey) L.H.Bailey
Rubus wisconsinensis L.H.Bailey
Sisyrinchium mucronatum Michx.

Andreas, B.K.  1995.  A floristic assessment system for Northern Ohio.  Technical Report WRP-DE-8 February 1995.  U.S. Army Corps of Engineers, Washington, D.C.

Herman, K.D., L. A. Masters, M. R. Penskar, A.A. Reznicek, G. S. Wilhelm, and W. W. Brodowicz (1996). Floristic quality assessment with wetland categories and computer application programs for the State of Michigan. Michigan Department of Natural Resources, Wildlife Division, Natural Heritage Program. Lansing, MI. 21 pp. + Appendices.

Nichols, S.A. 1998.  Floristic quality assessment of Wisconsin lake plant communities with example applications.  Journal of Lake and Reservoir Management 15:133-141.

Northern Great Plains Floristic Quality Assessment Panel. 2001. Floristic quality assessment for plant communities of North Dakota, South Dakota (excluding the Black Hills), and adjacent grasslands.  Jamestown, ND: Northern Prairie Wildlife Research Center Home Page. (Version 26JAN2001).

Oldham, M.J., W.D. Bakowsky, and D.A. Sutherland. 1995. Floristic quality assessment system for southern Ontario.  Natural Heritage Information Centre, Ontario Ministry of Natural Resources, Peterborough, Ontario.

Swink, F. and G. Wilhelm (1994). Plants of the Chicago Region, 4th ed., Indiana Academy of Science, Indianapolis, 921 pp.

Taft, John B., G.S. Wilhelm, D.M. Ladd, and L.A. Masters (1997). Floristic Quality Assessment for Vegetation in Illinois, A Method for Assessing Vegetation Integrity. In Erigenia, Number 15, November 1997.

Wilhelm, G. S. and L. A. Masters (1995). Floristic Quality Assessment in the Chicago Region and Application Computer Programs, Morton Arboretum, Lisle, IL. 17 pp. + Appendices.

Funding for the development of the Wisconsin Floristic Quality Assessment method was provided to the Wisconsin Department of Natural Resources by the U.S. Environmental Protection Agency under assistance agreement CD 97511501.  The contents of the WFQA and this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

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