Elsevier

Ecological Indicators

Volume 34, November 2013, Pages 260-267
Ecological Indicators

Floristic quality assessment signals human disturbance over natural variability in a wetland system

https://doi.org/10.1016/j.ecolind.2013.05.012Get rights and content

Abstract

A common concern regarding the popular Floristic Quality Assessment (FQA) method is whether the site floristic quality scores change with natural temporal and site-specific variability. The more ignored question is whether this background variability will confound the index of human disturbance. Using non-forested seasonal wetlands in the northeastern United States, we tested if two common indices of site floristic quality (FQAI, Mean CoC) provide clear signals of site condition relative to gradients of wetland area and surface water depth, and consistent signals across time of year (early vs. late growing season), geomorphic setting (connected vs. isolated), and vegetation community type (pine barrens vernal pond, wet sedge meadow, shrub swamp). Mean CoC is the coefficient of conservatism (a qualitative estimate of species’ sensitivity to human disturbance) averaged across the native and exotic taxa observed at a given site, and FQAI is the traditional Floristic Quality Assessment Index where Mean CoC is multiplied by square root of taxa richness. The FQAI did not linearly correspond to the site condition gradient and thus it could not be evaluated. Mean CoC was clearly associated with site condition, with no interference from wetland area or water level (based on computer-intensive resampling of linear model fit). Mean CoC also varied consistently with site condition between the surveys, geomorphic settings, and community types (based on computer-intensive resampling of linear model slope). However, connected wetlands showed inherently greater Mean CoC than isolated wetlands, suggesting a comparison of floristic quality between these categories would not be prudent. Overall this study suggests that FQA in the form of Mean CoC may withstand natural variability in certain non-forested wetland systems. Instead of assuming FQA is overly sensitive to natural variability, we recommend further efforts to identify situations in which FQA is robust.

Introduction

Floristic Quality Assessment (FQA) was originally developed in the late 1970s to assess prairies and open, undeveloped lands in the Lower Lake Michigan region of the United States (Swink and Wilhelm, 1994, Wilhelm and Ladd, 1988). Now FQA is used in over two-thirds of the United States (Medley and Scozzafava, 2009, Bried et al., 2012) in a variety of ecosystems, and has been applied in Canada (Francis et al., 2000) and in other countries (Landi and Chiarucci, 2010, Tu et al., 2009). It is an especially popular tool for wetland condition assessments and has been applied in wetland systems ranging from Virginia bottomland forests (Nichols et al., 2006) to Louisiana coastal marshes (Cretini et al., 2012) to North Dakota prairie potholes (Mushet et al., 2002). Several wetland FQA studies have rigorously evaluated index properties and performance (Bourdaghs et al., 2006, Ervin et al., 2006, Matthews et al., 2005), and a growing number of wetland monitoring programs are using FQA as part of multi-metric condition assessments (e.g., Hargiss et al., 2008, Mack, 2007, Reiss et al., 2010).

Accuracy of FQA depends on experienced botanists who assign a coefficient of conservatism (CoC) meant to capture a species’ ecological amplitude (sensu Packham and Willis, 1976) and sensitivity to human disturbance. The coefficients range from 0 to 10 with tolerant weedy species receiving the lowest scores and conservative species (sensitive to habitat degradation, “remnant-dependent”) the highest (Swink and Wilhelm, 1994, Taft et al., 1997). A complete or representative checklist of vascular flora is required for the area of interest, and the index is often the Mean CoC weighted by species richness or the Mean CoC alone (Rooney and Rogers, 2002, Spyreas et al., 2012, Taft et al., 2006).

A basic principle of FQA is that it reflects human disturbance or site condition with minimal ecological interference (Taft et al., 1997). Indeed, a challenge for any wetland assessment method is to ensure that measurements are related to functioning or condition of the wetland and not natural temporal or spatial variability (Brazner et al., 2007, Rader et al., 2001, Stein et al., 2009, U.S. EPA, 2002). However, in practice such factors as habitat type, site area, and seasonality of vegetation could bias the index or reduce its precision (Bourdaghs et al., 2006, Cohen et al., 2004, Ervin et al., 2006, Matthews, 2003, Matthews et al., 2005, Miller and Wardrop, 2006). This is often due to the inclusion of species richness as a component of FQA (Matthews, 2003, Matthews et al., 2005, Miller and Wardrop, 2006). Users of FQA may avoid or mitigate such problems by grouping sites according to environmental similarity and restricting surveys within narrow time frames of the growing season. Of course doing so may reduce a project's flexibility, increase its complexity, and force practitioners to make subjective judgments about perceived environmental categories and gradients. We think the issue deserves further scrutiny.

Several studies have found FQA metrics to vary across natural environmental categories or gradients (e.g., Andreas et al., 2004, Bried and Edinger, 2009, Euliss and Mushet, 2011, Taft et al., 2006), leading to a general assumption that FQA is overly sensitive to natural variability. An important question is whether this background variability overwhelms the disturbance signal. For environmental gradients (i.e., continuous variables such as area or depth), a signal to noise ratio could be measured as strength (model fit) of the expected linear relationship between floristic quality and increasing human disturbance (Andreas et al., 2004, Cohen et al., 2004, Lopez and Fennessy, 2002, Miller and Wardrop, 2006, U.S. EPA, 2002) relative to strength of the relationship between floristic quality and the underlying gradient. Alternatively, the floristic quality residuals from a regression over disturbance could be analyzed for a linear relationship to the natural gradients. For environmental categories (e.g., habitat type), the slope and not just the intercept of the relationship between floristic quality and disturbance is of interest and could be compared among categories. If the signal strength is weak or if the slopes intersect, then inference pooled over gradients or categories may indeed be biased or imprecise as generally assumed.

Wetlands are a good study system for this problem because they are extremely dynamic and variable (Mitsch and Gosselink, 2007), and because FQA is popular for wetland assessments. The goal of this paper is to evaluate the influence of natural variability on wetland FQA. Specifically, we test if two common indices of site floristic quality provide clear signals of site condition relative to gradients of wetland area and surface water depth, and consistent signals across time of year (early vs. late growing season), geomorphic setting (connected vs. isolated), and vegetation community type (pine barrens vernal pond, wet sedge meadow, shrub swamp).

Section snippets

Study area

Study sites were located in three unique areas of upstate New York (map in Bried and Edinger, 2009): Albany Pine Bush Preserve (hereafter “Pine Bush”), Rome Sand Plains, Wilton Wildlife Preserve & Park (hereafter “Wilton Preserve”). The Pine Bush is located in an urbanized landscape matrix whereas Rome Sand Plains and the Wilton Preserve reside in less modified exurban settings. The region is characterized by a cold-temperate humid climate with approximately 100 cm of mean annual precipitation

Results

A cumulative total of 153 vascular plant taxa were found across the sites and survey occasions. Of these, 128 taxa were identified to specific or infraspecific levels, which included 11 exotic species. Two additional taxa identified only at the generic level could also be used (i.e., 130 taxa for analysis) because one was exotic (Sonchus), thus CoC = 0 automatically, and the other was keyed out to two species possibilities (in Verbena) with the same CoC.

Using a Mantel correlation test with the

Discussion

Natural variability and ecological interference is a significant concern for application of the FQA approach to site quality assessment, including regulatory assessment of wetland condition. An important question is whether the relationship between floristic quality and human disturbance is stronger than the influence of underlying natural variability. Our study finds that FQA in the form of average species conservatism (Mean CoC) can signal human disturbance over natural variability. It

Acknowledgments

We thank Amanda Dillon and Arianne Messerman for helping with vegetation surveys, and the many volunteers (especially Barb Hager and Grace Barber) who helped monitor water levels. We also thank the Albany Pine Bush Preserve Commission, the Wilton Wildlife Preserve & Park, and The Nature Conservancy Eastern New York Chapter for site access and their interest in the project. The manuscript has benefitted greatly from the insightful criticism provided by several anonymous reviewers. Financial

References (58)

  • J.T. Bried et al.

    Baseline floristic assessment and classification of pine barrens vernal ponds

    J. Torrey Bot. Soc.

    (2009)
  • J.T. Bried et al.

    Comparison of herbicide treatments to control native aspen encroachment in pine barrens

    Nat. Areas J.

    (2011)
  • J.T. Bried et al.

    Coefficients of conservatism for the vascular flora of New York and New England: inter-state comparisons and expert opinion bias

    Northeast. Nat. Spec. Issue

    (2012)
  • M.M. Brinson

    A hydrogeomorphic classification for wetlands

    Wetlands Research Program Technical Report

    (1993)
  • R.T. Brooks

    Weather-related effects on woodland vernal pool hydrology and hydroperiod

    Wetlands

    (2004)
  • L.A. Brudvig et al.

    Evaluation of central North American prairie management based on species diversity, life form, and individual species metrics

    Conserv. Biol.

    (2007)
  • S.J. Chamberlain et al.

    Developing coefficients of conservatism to advance floristic quality assessment in the Mid-Atlantic region

    J. Torrey Bot, Soc.

    (2012)
  • M.J. Cohen et al.

    Floristic quality indices for biotic assessment of depressional marsh condition in Florida

    Ecol. Appl.

    (2004)
  • K.F. Cretini et al.

    Development and use of a floristic quality index for coastal Louisiana marshes

    Environ. Monit. Assess.

    (2012)
  • G.E. Crow et al.
    (2000)
  • E.S. Edgington et al.

    Randomization Tests

    (2007)
  • G.J. Edinger et al.

    Ecological Communities of New York State

    (2002)
  • G.N. Ervin et al.

    Evaluating non-native species and wetland indicator status as components of wetlands floristic assessment

    Wetlands

    (2006)
  • N.H. Euliss et al.

    A multi-year comparison of IPCI scores for prairie pothole wetlands: implications of temporal and spatial variation

    Wetlands

    (2011)
  • D. Faber-Langendoen et al.

    Developing Options For Establishing Reference Conditions for Wetlands Across the Lower 48 States

    (2009)
  • M.S. Fennessy et al.

    An evaluation of rapid methods for assessing the ecological condition of wetlands

    Wetlands

    (2007)
  • C.M. Francis et al.

    Assessing floristic quality in southern Ontario woodlands

    Nat. Areas J.

    (2000)
  • H.A. Gleason et al.

    Manual of Vascular Plants of Northeastern United States and Adjacent Canada

    (1991)
  • C.A. Johnston et al.

    A unifying approach for evaluating the condition of wetland plant communities and identifying related stressors

    Ecol. Appl.

    (2009)
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