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Plant distributions along salinity and tidal gradients in Oregon tidal marshes
Janousek, C. N., C. FOLGER, AND H. LEE, II. Plant distributions along salinity and tidal gradients in Oregon tidal marshes. Presented at Modeling and Planning for Sea Level Rise in the Pacific Northwest Workshop, Newport, OR, February 01 - 02, 2011.
Accurately modeling climate change effects on tidal marshes in the Pacific Northwest requires understanding how plant assemblages and species are presently distributed along gradients of salinity and tidal inundation.
Accurately modeling climate change effects on tidal marshes in the Pacific Northwest requires understanding how plant assemblages and species are presently distributed along gradients of salinity and tidal inundation. We outline on-going field efforts by the EPA and USGS to determine: (1) the degree to which National Wetlands Inventory tidal marsh classes correspond with specific marsh assemblages, (2) how intertidal elevation and estuarine salinity patterns correlate with the presence or absence of plant species and assemblages, and (3) the spatial distribution of common marsh taxa and total plant diversity within and among Oregon’s coastal estuaries. Data on plant composition, abundance and diversity, collected from over 160 plots in Yaquina Bay, Alsea Bay, Netarts Bay and Coquille Estuary in Oregon are being paired with data on intertidal elevation, soil salinities, and sediment grain size to determine relationships between marsh plant communities and abiotic factors. Preliminary findings suggest that the flora of these Oregon tidal marshes is highly diverse, with individual estuaries hosting dozens of taxa and individual plots (0.25 m2) supporting as many as 6-11 vascular plant species. Several species such as Deschampsia caespitosa, Juncus arcticus var. balticus, Agrostis sp(p). and Sarcocornia pacifica are widespread (high frequency of occurrence). Many other species are less common or are only minor components of the flora, but add to overall diversity. The occurrence of many of the more common plant taxa appears to be strongly linked to intertidal elevation. Additionally, overall plant diversity increases from lower to higher intertidal elevations. Both findings suggest that future sea level rise, absent net vertical accretion or horizontal migration, will shift plant distributions up the intertidal and/or away from the coast and lower diversity within some marshes. Salinity dynamics are currently being studied by deploying salinity loggers in marsh habitat, collecting water samples from marshes during high spring tides, and by conducting cruises in small tributaries linking marshes. Preliminary findings from Poole Slough in Yaquina Bay suggest strong spatial and seasonal variation in estuarine salinity as well as vertical stratification. By better linking specific marsh assemblages and individual species to salinity and elevation gradients, more specificity can be added to sea level rise models such as SLAMM to evaluate potential future changes to marsh structure and function.