“Spatial relationships for vegetation and soils in restored and remnant salt marshes in the Salmon River Estuary, Oregon”

Background/Question/Methods: This study investigated spatial patterns of species diversity in salt marsh vegetation and how vegetation and soils of remnant and restored marshes differ after 40 years of restoration on the Oregon coast. Vegetation surveys of 1m x 1m plots were conducted along previously-established transects of salt marsh vegetation surveys for four sites; three restored salt marshes and one remnant site. In addition, vegetation data were collected from three 20m x 50m modified Whittaker plots at each site. For each modified Whittaker plot, species presence-absence data were recorded for the entire plot and the 20m x 5m central subplot, and presence as well as abundance (visual estimates of percent cover) were recorded for all subplots (1 m², 10 m²). These data were then used to calculate species-area and species-accumulation curves. Soil samples were collected at transect plots and processed per National Soil Survey Center protocol for analysis of pH, bulk density, salinity, conductivity, and carbon/nitrogen content. The data were used to compare spatial patterns in vegetation diversity in restored vs. remnant salt marshes. In addition, the data were used to explore relationships between soil characteristics (bulk density, salinity, conductivity) and vegetation, and to compare remnant and restored sites.

Results/Conclusions: Preliminary results indicate significant differences between the vegetation of remnant and restored tidal marshes surveyed, based on restoration history. Outcomes suggest that remnant marshes are more heterogenous in species composition. In restored marshes, species such as Carex lyngbyei tend to dominate the sites with high frequency of occurrence and percent cover. Salt-tolerant species, such as Triglochin maritima and Sarcocornia perennis are associated with higher salinity/conductivity and low elevation conditions, while high marsh species, including Argentina egedii and Agrostis stolonifera are associated with higher elevations and lower salinities. Marsh surface elevation does not differ significantly among sites that were restored at different times in this estuary. The highest soil salinities occur in mid-marsh elevations where evaporation is higher than for high marsh plots which are only occasionally inundated or plots near the water’s edge (which are inundated at similar frequencies but longer time periods than as mid-marsh). Vegetation of restored salt marshes is significantly less diverse and more spatially homogenous than that of reference sites, even 38 years post-restoration. Site hydrology, time since restoration, and prior land-use history influence the vegetation community composition at Salmon River Estuary.