TESTING THE FLORISTIC QUALITY ASSESSMENT INDEX AS AN INDICATOR OF WETLAND CONDITION

Biological indicators of ecosystem integrity are increasingly being sought for use in ecosystem ashessment and goal-setting for restoration projects. We tested the effectiveness of a plant community-based bioassessment tool. the floristic quality assessment index (FQAI) in 20 depressional wetlands in Ohio, USA. A priori. the 20 depressional wetlands were classified by type and ranked to form a disturbance gradient according to the local landscape condition. Ranks were based on surrounding land~cover characteristics. vegetated buffer characteristics. and the extent of human-induced hydrologic alteration at the wetland site. The index was negatively correlated with the disturbance rank of a wetland and with the distance to neighboring wetlands ( P = 0.01). Index values were lower for wetlands surrounded by agricultural or urban land use. wetlands with less vegetation on the wetland perimeter. and wetlands with more hydrologic modification. and at sites with greater distances to other wetlands. The wetlands with lower FQAI values tended to be dominated by plants that are typical of heavily cultivated landscapes or urban regions. Thus. the index is interpreted as a measure of environmental factors that maintain and control plant communities. The index was not correlated with differences in wetland surface water chemistry (a= 0.05) but was positively correlated with soil total organic carbon ( P = 0.01). phosphorus ( P = 0.05). and calcium ( P = 0.05). Repeated wetland sampling in the summer and autumn revealed that the floristic quality assessment index could be useful for the assessment and monitoring of wetland ecosystems and for tracking wetland restoration projects over time. Key \~.orcf.s: biological it~dicaror; cfepressionnl ~ ,e t land: et~~,irontnet~rnl gracfient; poristic cl~rality assessnlent inc1e.x (FQAI): hi~rnnn influence; landscape-scale: stressor; wetlancf conefirion. scape and the embedded ecosystem, particularly when Patterns of ecosystem response to landscape change several parameters are simultaneously compared (Yodhave been postulated (e.g., Harris 1984. Opdam et al. er 1991, Karr and Chu 1997). As an alternative. some 1993, Forman 1995). but such relationships have usubiologists have measured aspects of plant community ally been studied in terms of an ecosystem's response composition, such as percent native species (Wilhelm to environmental extremes, rather than as a response and Ladd 1988. Adamus and Brandt 1990). This apto a gradual transition in land cover, hydrology. or proach is also inadequate. because it excludes details patchiness. Some of the relationships between landof plant community structure. such as taxa that have scape stressor and aquatic plant community composispecific physiological requirements. A floristic quality tion have been explored in lakes of Nova Scotia and assessment index (FQAI: index, hereafter). developed the Pyrenees Mountains by measuring stressor gradifor prairies by Swink and Wilhelm (1979) offers several ents among sites, thus relating landscape conditions to features that might improve upon the above indicators the structure of nearby biological communities (Catling of ecosystem integrity. The index is based on expert et al. 1986, Gacia et al. 1994). The gradient technique. knowledge of each plant species' tendency to occur in however. requires a priori pairing of "stressor" varia range of existing synecological conditions (Andreas ables with "response" variables to be ecologically and Lichvar 1995). To use the index. each plant species meaningful. This approach may obscure the relationat a site is given a ranking based on the likelihood of ships between the biological components of the landthat species being encountered at disturbed sites of a region. The index is calculated for a site (e.g., a wetManuscript received 28 February 2000: revised 24 January land) by summing these ranks, and dividing by the 200 1 : accepted 7 Februarj 2001. square root of the number of native plant species at the Present address: U.S. Environmental Protection Agencv site (Andreas and Lichvar 1995). We chose to test the " National Exposure Research Laboratorj, Environmental Sciability of the index to characterize depressional wetence Division. Office of Research and Development. P.O. Box lands in because plant assemblages in 93478, Las Vegas, Nevada 89193-3478 USA. these wetlands receive much of the local runoff from E-mail: lopez.ricardoOepa.gov J present K~~~~~ ~ ~the surrounding landscape and are likely to integrate ~ ~ ~ colleEe. ~of ~ i ~ l ~ t -~ " ogy, Gambien Ohio 43022 USA. the effects of stress from the local landscape. A pre488 RICARDO D. LOPEZ AND M. SIOBHAN FENNESSY Ecological Applications Vol. 12, No. 2 vious study of 10 forested riverine wetlands in central Ohio demonstrates a negative correlation between the index value of a site and the degree of site disturbance (Fennessy et al. 1 9 9 8 ~ ) . In this study. we specifically tested the ability of the index to characterize wetland site disturbance and isolation. focusing on plant biomass production. water chemistry, and soil chemistry. The Ohio subsample included depressional wetlands that range from highly impacted (e.g., wetland remnants on farmland) to less impacted (e.g., wetlands within nature preserves). The objective was to compare the index values of 20 wetlands to the type and intensity of local landscape condition. Prior ecological assessments suggest that three fundamental factors are responsible for wetland ecosystem stress: land cover change in the vicinity of a wetland. the presence of a vegetated "buffer" between adjacent land cover and the wetland. and the hydrologic conditions within the wetland (U.S. Environmental Protection Agency 1994). Thus, these three landscape parameters were used to determine the relative site disturbance among the 20 wetland study sites. Prior research also suggests that the distance between ecosystem patches is a limiting factor for wetland plant dispersal (Godwin 1923. Nip-van der Voort et al. 1979, Moller and Rordam 1985. Lopez 1999), so the proximity of wetland study sites to neighboring wetlands was used as a potential landscape-scale wetland stressor. Plant biomass often reflects ecosystem condition. because it integrates the effects of many ecological processes (Vitousek and Reiners 1975, Keddy et al. 1993, Wilcox 1995). Plant biomass production may therefore indicate wetland stress and was specifically tested for correlation with the index. Site physiochemical characteristics are also important to consider when determining landscape-level effects on plants (Chapin 1991. Salisbury and Ross 1992. Larcher 1995). Therefore, water and soil chemistry of depressional wetland study sites were tested for correlation with the index