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RESPONSE OF WETLAND PLANT SPECIES TO HYDROLOGIC CONDITIONS
Citation:
Magee, T. K. AND M E. Kentula. RESPONSE OF WETLAND PLANT SPECIES TO HYDROLOGIC CONDITIONS. Wetlands Ecology and Management. Springer Science and Business Media B.V;Formerly Kluwer Academic Publishers B.V., , Germany, 13:163-181, (2005).
Description:
Understanding hydrologic requirements of native and introduced species is critical to sustaining native plant communities in wetlands of disturbed landscapes. We examined plant assemblages and 31 species from emergent wetlands in an urbanizing area of the Pacific Northwest, USA, in relation to in situ, fine-scale hydrology. Percent cover by plant species was estimated in 2208 1-m2 plots across 43 sites, with water depth at time of vegetation sampling (WDS) measured in 432 plots. Three years of bi-weekly hydrologic data from each site, were used to estimate mean surface water level (SW) and mean absolute difference in surface water level (MAD) for every plot. Nine assemblages of plant species that co-occur in the field were identified (TWINSPAN). The assemblage richest in native species occurred under intermediate hydrologic conditions and was bracketed by pasture grass dominated assemblages at drier conditions with low water level variability, and Phalaris arundinacea assemblages with higher mean water levels and variability. Results suggest minor changes in average water levels 10 cm) or in variability (?2 cm in MAD) could promote a shift from assemblages dominated by natives to those dominated by invasive or alien taxa. lndividual species segregated into four groups along CCA defined axes related to hydrologic gradients. Each species response group was typified by taxa with similar optima (mean position indices (ei)) for a given environmental variable (WDS, SW, MAD), with each group related to a characteristic suite of hydrologic conditions. The most common species (P. arundinacea, Juncus effusus, and Typha latifolia), each representing a different response group, exhibited unique responses in occurrence/abundance in relation to water level variability, but were abundant over a wide range of water depth. The realized niches of other species in each response group were more restricted, with peaks in cover confined to narrower ranges of water depth and variability.