Date Awarded

2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

James E. Perry, III

Abstract

We applied the Floristic Quality Index (FQI) to vegetation data collected across a chronosequence of created wetland (CW) sites in Virginia ranging in age from one to 15 years post-construction. at each site, we also applied FQI to a nearby forested reference wetland (REF), for a total of 30 sites (15 created, 15 reference). We tested the performance of the index against a selection of community metrics (species richness, diversity, evenness, percent native species) and site attributes (age, soil physiochemical variables). The relationship between FQI and community and environmental variables was analyzed with Spearman's rank order correlation coefficient and Canonical Correspondence Analysis (CCA). Calculation of FQI with all species (including non-natives) did not increase the number of significant correlations (p<0.05) with community attributes and/or environmental parameters when compared with FQI based on native species alone. Further, vegetation layer-based FQI calculations improved the sensitivity of the index to differences in floristic quality between sites when compared with an "overall" index calculated across layers, and a modified, abundance-weighted FQI showed a unique correspondence with community and environmental variables in the CW herbaceous layer and REF herbaceous and shrub-sapling layers. These results suggest that a "natives only", layer-based version of the index should be used in wetland assessment in Virginia, and an abundance-weighted FQI may be a useful tool for assessing floristic quality in certain layers. An abundance-weighted format is perhaps desirable because such an index preserves the "heritage" aspect of the species conservatism concept inherent in floristic quality assessment, and also entrains the "ecology" aspect of site assessment based on relative abundances of the inhabiting species. FQI did not successfully relate CW sites to REF sites, bringing into question the applicability of the FQI concept in comparing created wetlands to reference wetlands, and the use of forested reference wetlands in general to assess vegetation development in created sites. Based on correlations with soil nutrient variables and ordination results, we propose a conceptual model of vegetation development in created wetlands described as the "Initial Conditions" model, which is expressed in terms of initial site conditions, soil chemistry, species diversity, and floristic quality.

DOI

https://dx.doi.org/doi:10.25773/v5-ps2s-j318

Rights

© The Author

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