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Plant Stewardship Index
INTRODUCTORY SECTIONS
The Plant Stewardship Index is a standardized assessment tool that calculates a numerical index
reflecting the quality of native plant communities for a given area. It indicates the impacts of invasive
plants and can also be used to monitor the efficacy of land management practices.
Summary
The Plant Stewardship Index (PSI) enables stewards of public and private land in the Piedmont area of
Pennsylvania to survey and assess the status of the native plant populations on the properties they
protect and manage. The PSI also serves as a broader ecological indicator in that the health of the native
plant community has been shown to correlate with water quality, macroinvertebrate diversity,
mammalian diversity, and overall watershed health. (PNPS 2003)
The PSI provides a method for monitoring and evaluating land management practices. This method,
adapted from the Floristic Quality Assessment Index (FQAI or FQI) methodology, assigns relative
values (Coefficients of Conservatism or CCs) to every plant found within a survey area, and calculates
an overall PSI value for each area. By applying the PSI to plant surveys repeated at regular intervals,
land managers can quantify the results of their land management practices and assess trends over time.
The Bowman’s Hill Wildflower Preserve maintains a free website-based PSI calculator
(www.bhwp.org/db) that automatically calculates the PSI values for any entered plant inventory, and
posts results on a free regional vegetative database. The PSI was developed by Bowman’s Hill
Wildflower Preserve with the help of many regional botanical experts.
Typical Users
Local governments
Nonprofit organizations
Individuals and businesses
Educators
Examples of Plant Stewardship Index users include:
 Nonprofit organizations: The D&R Greenway Trust (http://www.drgreenway.org), Hunterdon
Land Trust Alliance (http://www.hlta.org), Duke Farms (http://www.dukefarms.org), Delaware
River Basin Commission (http://www.state.nj.us/drbc), Buckingham Friends School
(http://www.bfs.org ) and Friends of High School Park (http://www.highschoolpark.org) use the PSI
in their conservation work.
 Individual and businesses: Princeton Hydro (http://www.princetonhydro.com) uses the PSI to
monitor a variety of projects, including a stormwater management project and a wetland mitigation
site. In addition, a number of private individuals use PSI to assess and develop management plans
for their property.
 Educators: The PSI methodology is being incorporated into the curriculum at Delaware Valley
College and is integrated into the NJ Land Stewardship Training program provided by Rutgers
University.
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Track Record:
The Floristic Quality Assessment Index (FQAI) was developed in the 1970’s by Floyd Swink and
Gerould Wilhelm for the assessment of tallgrass prairie restorations in the Chicago area. It is widely
used by the Army Corps of Engineers, the EPA and all the various states who currently have
conservatism values assigned to their vascular flora. The PSI builds on the floristic quality assessment
formulas by adding data about non-native species to the calculation. Both FQAI and PSI are based on
the concept of species conservatism, and the assignment of Coefficients of Conservatism to a regional
floral by a panel of experts. Coefficients have been assigned to the vascular flora of the Piedmont area of
Pennsylvania and to the Upper Penn’s Creek area in central PA, as well as to Ohio, Colorado, Florida,
Mississippi, the Dakotas, Illinois, Michigan, Virginia, West Virginia, Missouri, Michigan, Iowa and
southern Ontario.
Bowman’s Hill Wildflower Preserve’s free database and PSI calculator now contains 334 plant lists
logged by over 150 account-holders. Account-holders include State and County Park managers, Nature
Center researchers, land trust stewards, academics, environmental advisory council members, private
schools, and private landowners.
Conservation Impact
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The public perception that preservation is successful once development has been halted is
incomplete: rather, our landscape is also under siege from deer predation and invasions of non-native
plants and insects. The extent to which there will be support for meaningful stewardship of these
dwindling resources will hinge on our ability to quantify these losses in quality to the public, and to
show the municipal decision-makers responsible for safeguarding these public trusts that we must
invest in meaningful stewardship to safeguard quality.
All plant lists may be viewed by all account-holders on the PSI website, creating a free interactive
floristic regional database that may be sorted by zip code, fostering real-time data interchange
amongst stewards in the public and private sectors.
The PSI can be used to assess trends
The PSI can be applied to existing data, such as plant inventories.
What You’ll Need
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A reasonable knowledge of field botany.
The PSI is a simple method using a plant inventory. It does not require expensive sampling
equipment or laboratory processing.
Challenges and Obstacles
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Since results may be strongly affected by observer expertise, studies must be carefully designed to
ensure comparability of results between observers; i.e. time and expertise levels should be
documented and replicated.
Some individuals or organizations may not have the time or expertise to conduct PSI surveys and
may need to hire a consultant.
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IN-DEPTH SECTIONS
Main Description
Introduction
A common goal of land stewardship projects is to preserve and protect those remnants of the natural
environment that remain relatively intact and to protect these sensitive areas from being adversely
impacted by human activities. A standardized assessment tool, such as the Plant Stewardship Index
(PSI) provides land stewards with the information they need to establish stewardship priorities and set
management goals. The PSI helps land stewards answer two questions: What is the naturalness of any
site? How have land management practices (or their absence) affected that naturalness over time?
Methodology
The PSI is based on the observation that plants may act as “generalists,” which are not particular about
where they grow and might grow very well on roadside ditches or in dooryards, as opposed to
“conservative” species, which may grow only in specialized habitats, such as serpentine barrens or the
pine barrens of New Jersey. For all of New Jersey and the Piedmont region of Pennsylvania, over 2000
plants have been catalogued and assigned a number from zero to ten by local experts and botanists.
Zero represents the most “generalist” species, tolerant of disturbance and includes invasive or introduced
nonnative species. Ten represents the most “conservative” species and includes many rare and
endangered state-listed native plants that require special habitats and do not regrow after disturbance.
This database of plants and associated numerical values are available to users through Bowman’s Hill
Wildflower Preserve’s PSI Calculator located at their website http://www.bhwp.org. Once a user inputs
a list of plants found on a particular site, the calculator automatically computes: (1) the Mean C, which
is the average of all the assigned numbers of plants found on a site, and (2) the Index number, which is
the Mean C multiplied by the square root of the total number of plant species.
Implementation
Overall Assessment or Analysis by Habitat Type or Management Unit
Prior to undertaking a PSI, stewards must decide whether they are interested in an overall assessment of
floristic quality, or in a more detailed analysis by habitat types or management units, in which case
individual inventories of each habitat or unit would be compiled. For example, a property might consist
of an upper meadow and riparian corridor adjacent to one another, but requiring potentially different
management regimes. In this case, separate inventories could be compiled for each section, allowing
each area’s quality to be tracked separately. The Bowman Hill Wildflower Preserve’s PSI calculator can
then run an aggregate computation for the total PSI values of the two areas considered together, thus
yielding an overall index value.
To determine if floristic quality is distributed more or less evenly throughout the site, or if some areas
are more degraded than others, quadrat plots may be sampled, either randomly or along a transect.
Commonly, a cover category or percent cover is assigned to each species within a quadrat, so that
importance values may also be calculated for each of the species present. Native and total mean C
values may fluctuate along the transect, as may percent native, relative importance and FQAI/PSI, all of
which will reflect changes in quality across the site. Another approach to the question of uniform
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floristic quality across a site would be to establish permanent sampling plots in representative portions
of a site with surveys that are repeated on a regular basis.
for the management of these public trusts.
Assigning Coefficients of Conservatism
To apply the PSI methodology, an inventory of the study area is done and each native taxon is assigned
a coefficient of conservatism (C), an integer from 0 to 10, termed a coefficient of conservatism (C),
which combines its tolerance to disturbance and its fidelity to a pristine or undisturbed habitat (remnant).
Species given a C-value of 0-1 are taxa adapted to severe disturbances, while species ranked with a Cvalue of 2-3 are associated with somewhat more stable, though degraded, environments. Those species
with coefficients of 4-6 include many dominant or matrix species for several habitats; they have a high
consistency of occurrence within given community types. Species with C-values of 7-8 are taxa we
mostly associated with natural areas, but that can be found persisting where the habitat has been
somewhat degraded. Those species with coefficients of 9-10 are considered to be restricted to highquality natural areas.
Coefficients of Conservatism are assigned by panels of experts familiar with their regional vascular
flora. Coefficients have been assigned to the vascular flora of the Piedmont area of Pennsylvania and to
the Upper Penn’s Creek area in central PA, as well as to Ohio, Colorado, Florida, Mississippi, the
Dakotas, Illinois, Michigan, Virginia, West Virginia, Missouri, Michigan, Iowa and southern Ontario.
Coefficients of Conservatism for the Piedmont area of Pennsylvania are available to download at
www.bhwp.org/db .
The Mean Native C value is a meaningful measure of habitat quality. It is not dependant on size of
inventory area and is thus a meaningful measure of native species richness. (Rooney + Roger. 2003) A
difference between native mean C and total mean C that is greater than 5 suggests that native flora has
been compromised by non-native species. (Rothrock and Homoya 2005) Introduced plants, by their very
nature, were uninvolved in the pristine native landscape, so Coefficients of Conservatism are not applied
to them. All non-native or adventive plants are given a C value of 0.
Calculation of the PSI
Calculation of the PSI formulas are difficult and may be beyond the skills of some users. To address
this concern, the free, accessible Bowman’s Hill Wildflower Preserve web-site automatically calculates
the PSI and FQAI values of any entered plant inventory, and allows the account-holder to print out
complete reports of the findings. An overview of the process used to calculate the PSI follows: The
naturalness of the total plant community is calculated by adding in all non-native species and giving
them a C value of 0. Thus Total Mean C can be computed, and the PSI value is calculated by
multiplying the Total Mean C by the square-root of N, where N is native species richness. The FQAI of
an area is computed by multiplying the Native Mean C by the square-root of N, where N is the native
species richness.
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Use of the PSI in Monitoring Habitat Restorations
When monitoring habitat restorations, if the management is efficacious, the Native Mean C either
stabilizes or gradually obtains its original value (Wilhelm + Taft. 2004) “Tracking the quality of
restorations and management efforts is well within the capabilities of preserve and federal land wildlife
managers when using the FQAI and PSI. As an example, if a wetland preserve ecologist were
implementing different techniques for restoring previously disturbed wetlands, changes in Native Mean
C values or FQAI over time could aid in determining which method is more effective in repopulating the
areas with desirable species.(Herman et al. 2006)
Available Resources
The database and PSI calculator are available to the public at no charge on Bowman’s Hill Wildflower
Preserve’s website at www.bhwp.org/db. Accounts are free and account-holders may compile and save
site lists, modify or update lists, track lists print reports and view all other users’ site lists.
Individuals or organizations without the time, expertise or resources to conduct PSI surveys may hire
Bowman’s Hill Wildflower Preserve to conduct a half-day or full-day inventory on a fee-for–service
basis. Most sites may be assessed with a professional half-day or a full-day survey, or a complete
floristic inventory may be produced by repeated surveys at various times throughout the year.
Individuals or organizations may attend educational courses at Bowman’s Hill Wildflower Preserve to
learn more about implementation of the PSI methodology or to enhance plant ID skills. These classes:”
Introduction to the Plant Stewardship Index”, and “PSI Field Training” workshop are offered repeatedly
throughout the year. See www.bhwp.org for current offerings.
Benefits of Using the PSI
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If the FQAI and the PSI of an area are the same, there are no non-native plants on the site. Thus, the
numerical difference between FQAI and PSI can reveal the extent of non-native impacts.
The PSI/FQAI ratio is simple – (based on either an inventory survey or a transect study), and as such
it is an excellent rapid assessment of biological integrity. (EPA Office of Water 2002)
The PSI can be used to determine the extent to which management (or lack thereof) is having an
effect on the floristic quality of a site.
FQAI/PSI can be effective in tracking vegetation changes in restoration, reconstruction, or control
situations. (Taft et al. 1997)
Land trusts and landowners can use these assessments to guide their stewardship on the ground,
while governmental oversight officials might use this data to set buffers and mitigation ratios. (In
Michigan and Illinois, “High Quality” wetlands (FQI ~ 35) must be mitigated at higher rates; 1:3 or
1:5 for example.)
The PSI is not meant to be a stand-alone test of habitat quality, but should be used in conjunction
with other measures of habitat quality. (Taft et al.1997; Hermann et al 1997) Floristic Quality
Assessment is a richness- weighted index of “natural quality” where natural quality is combination
of tolerance to disturbance, and habitat fidelity to pristine or undisturbed habitat. These two metrics
have particular relevance to conservation decision-making.
PSI inventory or transect will yield data used to calculate the following parameters: 1) species
richness – both native and introduced 2) floristic quality index 3) plant stewardship index ( FQAI
with introduced species) 4) mean native coefficient of conservatism 5) mean total coefficient of
conservatism 6) guild diversity 7) species relative importance 8) percent native and 8) wetness
characteristics.
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Use of FQAI and PSI in Permitting, Performance Standards, and Mitigation
FQAI and PSI can be useful in the application of resource protection laws. Two examples follow:
Detroit Airport Expansion
The following is an example excerpted from Herman (1994) where the FQAI system was used as a
performance standard and for establishing mitigation criteria in an endangered species permit for the
Detroit Metropolitan Wayne County Airport expansion:
In 1989, expansion of the Detroit Metro Airport was expected to result in the on-site loss of three
plant species listed as threatened under the M-ESA. The three species were Aristida longispica
(slender three-awned grass), Juncus brachycarpus (short fruited rush), and Ludwigia alternifolia
(seed box). The three species were found within remnant lakeplain wet-mesic prairies and mesic sand
prairies. The statutory requirements of Part 365 (Endangered Species Protection) of P.A. 451 of 1994
were enhanced by making compliance with this act a condition of the state wetland permit. The
provisions of the endangered species permit allowed the translocation of affected plants and seed bank
to an off-site location, which had been excavated and graded to match the land contours and hydrology
of the airport site. Unaffected areas on the airport were required to be protected and monitored as a
baseline to compare the success of the translocated plants. Hydrology, soil moisture, and vegetation are
being monitored for ten years.
The criteria for success, required by the permit, states that at the off-site mitigation location,
populations of threatened plants must be at least as large and viable as populations eliminated by the
airport expansion. In addition, the mitigation area is required to be free of aggressive weeds such as
Lythrum salicaria (purple loosestrife), the species diversity index should be stable or show an increase in
native species diversity throughout the monitoring period, and it should show a stable or increasing
floristic quality index and mean coefficient of conservatism.
DuPage County Stormwater and Flood Plain Ordinance
DuPage County, Illinois in implementing its stormwater and flood plain ordinance uses a C= 3.5 as
a criteria for identifying “critical” wetlands and requires mitigation for the loss of these wetlands in
the form of 3:1 acre wetland replacement (DuPage County Stormwater Management Committee,
1992). Administrative rules to the Illinois Wetland Policy Act of 1989 (20 ILCS 830, 17 Ill. Adm.
Code 1090) also requires a 5.5:1 replacement ratio for mitigating loss of wetlands with a native
floristic quality greater than 20 (FQI ≥ 20) or a mean coefficient of conservatism greater than or
equal to 4 (C ≥ 4.0). Wilhelm (1991, 1992, 1993) suggests, based on monitoring data obtained from
Chicago region restoration sites, that areas with known high floristic quality (FQI ≥ 35) cannot be
routinely restored to their original floristic quality and therefore are immitigable. Conversely, lower
quality wetlands registering FQAI in the teens and twenties may be mitigable
History
The PSI methodology was created in the 1970s in the Chicago region by Floyd Swink and Dr. Gerould
Wilhelm and has been developed in many other states as the Floristic Quality Assessment Index (FQAI).
Acknowledgements
Thanks to Leslie Jones Sauer, Tama Matsuoka, Ann Rhoads, Jack Holt, Janet Ebert, Linda Kelly, Bill
Olson, Emile DeVito, Mary Leck, Karl Anderson, David Snyder, Kathleen Walz and Gerould Wilhelm
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for their generous assistance and expertise in helping to guide the development of the Plant Stewardship
Index by Bowman’s Hill.
Alternatives to and Concerns about the Plant Stewardship Index
There are alternatives to the Plant Stewardship Index that users may want to consider. Some of these
other approaches may offer more scientific rigor. See “Concerns about the Plant Stewardship Index and
the Floristic Quality Assessment methodology and applications in general” [HYPERLINK TO
LIBRARY ITEM] prepared by Ann Rhoads of the Morris Arboretum (1/26/07).
Publications and Links
Native Plants and Their Role in the Upper Penn’s Creek Watershed
http://www.pawildflower.org/g3/00_intro/intro.htm
Describes a Growing Greener funded project whose focus of this project was to investigate the role of
native plants in the Upper Penns Creek watershed and their relationship to water quality.
Bernthal, Thomas W.: 2003. Development of Floristic Quality Assessment Methodology for Wisconsin.
Final Report to USEPA Wetland Grant # CO975115-01-0 Wisconsin Bureau of Fisheries Management
and Habitat Protection.
http://dnr.wisconsin.gov/org/water/fhp/wetlands/documents/FQAMethodWithAcknowledgements.pdf
See pages 6-7 for discussion of sampling timing on Mean C and FQA Index scores.
Bourdagh, Michael: The Relationship between Sampling Area, Species Richness and the Floristic
Quality Assessment Index. University of Minnesota, Natural Resources Research Institute.
http://www.conbio.org/Activities/Meetings/2003/website/poster.htm#P005-012
Description of poster done for a Society for Conservation Biology meeting. Describes a critical analysis
done on the FQAI and includes contact information.
Herman, Brook D., Madsen, John D, Ervin, Gary N.: Development of Coefficients of Conservatism for
Wetland Vascular Flora of North and Central Mississippi; GeoResources Institute Report 4001 (Water
Resources) March 20, 2006
http://www.cdfinc.com/CRI/Mississippi%20FQA.pdf
Provides information on the history of the FAQAI, and the development and use of CCs
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, Michigan. 21pp +
Appendices.
http://epa.gov/greenacres/mi-list.html
Applications of this system include the identification of remnant habitats of native floristic significance,
comparisons between different sites, long-term monitoring of floristic quality, monitoring the progress
of habitat restoration, and the use of National Wetland Categories to assist in identification of wetlands.
The MDNR is using the same quality assessment system that Floyd Swink and Gerould Wilhelm used
for the Chicago Region.
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The website has ordering information for copies of this publication with the computer program
application
Mushet, David M., Ned H. Euliss, Jr., and Terry L. Shaffer. 2002. Floristic Quality Assessment of one
natural and three restored wetland complexes in North Dakota, USA. Wetlands 22(1):126138. Jamestown, ND: Northern Prairie Wildlife Research Center
Online. http://www.npwrc.usgs.gov/resource/wetlands/ndwetlnd/index.htm
Swink, F. and G. Wilhelm. 1979. Plants of the Chicago Region. The Morton Arboretum, Lisle, Illinois.
Swink, F. and G. Wilhelm. 1994. Plants of the Chicago Region. 4th ed. Indiana Academy of Science,
Indianapolis.
Taft, John B. and G. Wilhelm, D.M. Ladd, and L.A. Masters. 1997. Floristic Quality Assessment for the
Vegetation of Illinois, A Method for Assessing Vegetation Integrity. In Erigenia, Number 15, November
1997.
http://www.pawildflower.org/g3/04_resources/Illinois_FQA.pdf
Tool Experts/Contacts
Jeannine Vannais
Bowman’s Hill Wildflower Preserve
PO Box 685
New Hope, PA 18938
215-862-2924
[email protected]
Vannais is the Plant Stewardship Index Coordinator at Bowman’s Hill Wildflower Preserve
Acknowledgements
The original text for this tool was prepared by Jeannine Vannais of Bowman’s Hill Wildflower Preserve.
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