The effects of urbanization on the structure, quality, and diversity of cypress plant communities in central Florida.

摘要

The integrity of wetland ecosystems is largely determined by hydrological functionality, degree of connectivity to like ecosystems, and permeability to external influence. Land use changes in upland areas adjacent to wetland ecosystems may influence hydrology and connectivity while introducing novel biotic and abiotic materials. There is an increasing trend toward the use of remote assessment techniques to determine the degree of impact of external influences on adjacent wetlands. Remote assessment and predictive capabilities are provided by indices such as the Landscape Development Intensity Index (LDI) (Brown and Vivas 2005) which may be beneficial in determining site condition, and which have the added benefit of providing a quantitative gradient of human impact. This study assessed the predictive ability of the LDI in cypress ecosystems, by testing its correlations with plant community metrics including an index of floral quality calculated using coefficients of conservatism (CC) (Cohen et al. 2004), plant species diversity, and fluctuation in community composition assessed by changes in the wetland status and native status of component plant species. LDI was also compared against an independent measure of disturbance which was used to construct an a priori disturbance gradient. Overall, diversity measures showed little correlation with any of the disturbance indices, while CC scores were significantly correlated. Models were constructed in an attempt to explain each of the variables of plant community response to development in the surrounding landscape. The length of time since the development of the land adjacent to the cypress domes was a predictor of plant community response only when included in models with other variables. LDI was the strongest predictor in all models except where increases in land use associated with hydrological changes helped predict or better predicted proportions of exotic and upland species.