| This 1996--1997 study determined the structure, composition, and above-ground productivity of Saginaw Bay coastal wet meadow vegetation, and the impact of hydrology, soils, anthropogenic disturbance, and Purple Loosestrife on this vegetation assemblage.;Groundwater, surface water, precipitation, and pan evaporation were monitored in a reference and disturbed wet meadow. Precipitation, seiche and storm surge inundation, and evapotranspiration controlled growing-season groundwater levels in un-flooded wet meadows. Mid-summer ET exceeded precipitation and storm surge inputs, lowering groundwater levels. Groundwater levels >60cm lower than Saginaw Bay were observed 20m from Saginaw Bay. Groundwater recharge occurred by vertical percolation, not horizontal groundwater inflow.;Fifteen of 93 species encountered contributed 84.0% of total vegetation importance value at 25 study sites. Calamagrostis canadensis, Carex aquatilis, Carex sartwellii, and Carex stricta contributed 60.1% of total IV. Twenty-seven species occurred in only one of 300 plots. The vegetation canopy was 1.2--1.5m tall, with half the leaves occurring 43--84cm above ground. There were three canopy layers, and vine-like species climbing among the three canopy layers.;Stem densities were greatest where mean mid-summer water levels ranged between +10cm and -10cm depth. Plot biomass and species richness peaked at greatest standing water levels due to the encroachment of marsh species. Anthropogenic disturbance altered these patterns. The vegetation exhibited identifiable lower and upper wet meadow sub-types. Thin peat and fitter mats, short hummocks, and small-stature species occurred more often in upper wet meadows, whereas thick peat and litter mats, tall hummocks, and physically larger wet meadow emergent species occurred more often in lower wet meadows.;Fluctuating surface- and groundwater levels had the greatest impact of any abiotic factor on the vegetation. Hydroperiod directly impacted vegetation composition, and strongly influenced the pattern of occurrence of other abiotic factors.;Mean peak wet meadow standing crop was 669g/m2. Growing-season fitter production was 152g/m2, and in-place litter decomposition was 186 g/m2. Net aboveground primary productivity was 1007g/m 2/yr.;There were few significant differences in the vegetation of either reference and disturbed, or Loosestrife and Loosestrife-free sites. The vegetation resisted anthropogenic disturbance impacts and Purple Loosestrife introduction, and exhibited resilience once disturbance ended. Soil disturbances (dredging, filling, excavation, and cultivation) were the most disruptive disturbance types. Wet meadow vegetation exhibited greater resilience following soil disturbance when hydrology was not disturbed. |
