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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. Presented at Society of Wetland Scientists 22nd Annual Meeting, Chicago, IL, May 27-June 1, 2001.
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 plant assemblages 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 suggests 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. Individual species segregated into four groups along CCA defined hydrologic gradients, and based on mean position indices (ei) of species for each hydrologic variable. The most common species (P. arundinacea, Juncus effusus, and Typha latifolia) each represented different responses based on 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 narrow ranges of water depth.