Floristic Development Patterns in a Restored Elk River Estuarine Marsh, Grays Harbor, Washington

Abstract

We describe the changes in the floral assemblage in a salt marsh after reconnection to estuarine tidal inundation. The Elk River marsh in Grays Harbor, Washington was opened to tidal flushing in 1987 after being diked for approximately 70 years. The freshwater pasture assemblage dominated by Phalarais arundinacea (reed canary grass) converted to low salt marsh vegetation within 5 years, with the major flux in species occurring between years 1 and 4. The system continued to develop through the 11-year post-breach monitoring period, although change after year 6 was slower than in previous years. The assemblage resembles a low salt marsh community dominated by Distichlis spicata (salt grass) and Salicornia virginica (pickleweed). Because of subsidence of the system during the period of breaching, the restored system remains substantially different from the Deschamsia cespitosa (tufted hairgrass)-dominated reference marsh. Use of a similarity index to compare between years and also between reference and restored marshes in the same year revealed that similarity in floral composition between year 0 and subsequent years decreased with time. However, there was a period of dramatic dissimilarity during years 1 to 3 when the system was rapidly changing from a freshwater to estuarine condition.Similarity values between the reference and restored system generally increased with time. Somewhat surprisingly the reference marsh showed considerable between-year variation in similarity, which indicated substantial year-to-year variability in species composition. Based on accretion rate data from previous studies we predict that full recovery of the system would take between 75 and 150 years.

Factors affecting the success of early salt-marsh colonizers: seed availability rather than site suitability and dispersal traits

“…Vegetation succession took place rapidly and within 5 7 years, the newly created mudflat became colonized with most adjacently appearing salt-marsh 8 species. The same pattern and progress was observed in an estuarine restoration site in the Elk 9 River Estuary, USA (Thom et al 2002), which was created by re-introducing a tidal 10 inundation regime to a former embankment area. Here, the largest increase in number of 11 species occurred 3 years after de-embankment and after 5 years species diversity was similar 12 to an adjacent reference marsh.…”

“…The presence of a salt marsh close to restoration sites appears to be a pre-requisite for 25 rapid regeneration and colonization of new salt marsh ; Thom et al 2002). …”

Guidelines, processes and tools for coastal ecosystem restoration, with examples from the United States

“…A growing body of evidence on constructed systems shows that most aquatic systems do not reach stability in less than 5 years (e.g., Simenstad & Thom 1996, Kentula 2000. Ecosystems of the size of most restoration projects take decades or centuries to develop (Frenkel & Morlan 1990, Boumans et al 2002, Crooks et al 2002, Thom et al 2002. Hence, we cannot expect restored systems to be stable in a year.…”

Protocols for Monitoring Habitat Restoration Projects in the Lower Columbia River and Estuary

“…Most organisms have specific tolerances for water parameter ranges or rates of change (fluctuations). For example, temperature is a good predictor of juvenile salmon abundance and condition (OWEB 1999) and salinity is a main determinant of vegetation patterns (Thom et al 2002). Oxygen concentration and pH can control the distribution of many organisms.…”

“…Plant community composition and cover can change rapidly following reconnection to a tidal hydrologic regime (Cornu and Sadro 2002;Roman et al 2002) especially if the reconnection fosters salinity intrusion (Thom et al 2002). Vegetation patterns confer both structural elements and ecological processes to wetland ecosystems, and may increase ecosystem capacity for foraging salmonids (Sommer et al 2001;Tanner et al 2002).…”