Abstract:
The purpose of this study was to determine plant species composition, community structure, successional relationships, vegetational development and plant distributions in estuarine salt marshes on the Pacific Coast of Oregon. Quadrat and transect samples of plant presence and cover, collected from April 1971 - June 1974, were subjected to phytosociological analysis and ordination, resulting in the identification of 6 salt marsh vegetation types comprised of 28 communities. The vegetation types include: Low Sand Marshes, Low Silt Marshes, Sedge Marshes, Bulrush and Sedge Marshes, Immature High Marshes and Mature High Marshes. The locations and extent of these types were mapped for 16 major Oregon estuaries. Total undiked salt marsh area in Oregon is 29 km2, an area significantly smaller than prior to diking and filling of marshlands. Three major patterns of plant succession were apparent, including those on sand and silt substrates and in areas subject to freshwater runoff, Carex 1 n b ei is an intermediate in all modes of succession, and this sedge typifies Oregon salt marshes in general. A few major species, including Triglochin maritimum, Salicornia virmica, Carex lyn b ei and Deschampsia caespitosa, rapidly accrete
sediments. The oldest carbon date obtained for undiked marsh was 770 f 85 years, Plant distributions were related to elevation, and phonology to tidal exposure and salinity, soil and soil water salinity, and water
table depths. In Oregon, salt marshes extend from above mean tide level upward to extreme high water level, Oregon coastal salt marshes are a transition between subarctic and temperature marshes, and are similar in physiognomy to boreal salt marshes in Scandinavia.
