Karen Thorne, US Geological Survey, and Christopher Janousek, Oregon State University, 2015-06-26, Vegetation Surveys, All Field Sites, 2012-2014: U.S. Geological Survey Data Release, http://dx.doi.org/10.5066/F7SJ1HNC .
Summary
We conducted vegetation surveys concurrently with elevation surveys at every fourth elevation point (~25% of the elevation points) (Figure 5). We visually assessed percent cover of all plant species within a 0.25 m2 quadrat, and recorded the average and maximum height (measured to the nearest centimeter) of each species. Total plant cover in a plot could exceed 100% due to vegetation layering. Vascular plant nomenclature generally follows Baldwin et al. (2012) and Cook et al. (2013). We located 69 tidal wetland species in 2,154 vegetation plots across the nine estuaries in the study. Common species included Carex lyngbyei, Sarcocornia perennis, Distichlis spicata, Deschampsia cespitosa, Juncus balticus and Potentilla anserina. The [...]
Summary
We conducted vegetation surveys concurrently with elevation surveys at every fourth elevation point (~25% of the elevation points) (Figure 5). We visually assessed percent cover of all plant species within a 0.25 m2 quadrat, and recorded the average and maximum height (measured to the nearest centimeter) of each species. Total plant cover in a plot could exceed 100% due to vegetation layering. Vascular plant nomenclature generally follows Baldwin et al. (2012) and Cook et al. (2013). We located 69 tidal wetland species in 2,154 vegetation plots across the nine estuaries in the study. Common species included Carex lyngbyei, Sarcocornia perennis, Distichlis spicata, Deschampsia cespitosa, Juncus balticus and Potentilla anserina. The frequency of several common species varied markedly across the sites. Distichlis spicata dominated the flora at five of the nine sites, but was relatively uncommon at Port Susan and Grays Harbor. Deschampsia cespitosa, a middle to high marsh tussock-forming species was frequent at the three Oregon sites and at Willapa but much less common in Puget Sound marshes. The high marsh rush, Juncus balticus, was most frequent at Siletz and absent or rare at Willapa and Padilla. Carex lyngbyei occurrence was variable regionally, ranging from >75% frequency at Bull Island to near absence at Padilla (it did not occur in any surveyed plots, but a few plants were observed at the upland margin of the site in late 2014). See appendices for detailed site specific results. We delineated marsh zones using long-term NOAA tidal data combined with our site-specific elevation and water level data and examined plant abundance in these major zones across the sites. At many sites, plant composition tended to vary by zone, but not necessarily in consistent ways across the region. For instance, at Bandon, Sarcocornia perennis was the most abundant high marsh species (with Deschampsia cespitosa most abundant in middle and low marsh), while S. perennis was the most abundant plant in low marsh at Grays Harbor (Carex spp. dominated in mid-marsh and Potentilla anserina dominated high marsh). Vertical zonation of plant assemblages was less pronounced at other sites, including Nisqually where Distichlis spicata had the highest mean cover in all three major marsh zones. Low marsh habitat was common at Bull Island, Willapa, Nisqually, and Port Susan. Common species in this zone included Sarcocornia perennis, Distichlis spicata, Carex lyngbyei, and Triglochin maritima. Middle tidal marsh was present at all of the sites and particularly common at Skokomish. Common species included all of the aforementioned taxa and Deschampsia cespitosa, Juncus balticus, and Agrostis stolonifera. High marsh was only common at Bandon, Siletz, Willapa, Grays Harbor, and Padilla. Common high marsh species included many species found in other zones, but also included Potentilla anserine and Atriplex prostrata. Transition zone habitat (defined as wetland flooding at least once per year but no more than once per month) was limited at most of our study sites. Zonation of individual species per site are illustrated in the respective appendices.
In the Pacific Northwest, coastal wetlands support a wealth of ecosystem services including habitat provision for wildlife and fisheries and flood protection. The tidal marshes, mudflats, and shallow bays of coastal estuaries link marine, freshwater and terrestrial habitats and provide economic and recreational benefits to local communities. Climate change effects such as sea-level rise are currently altering these habitats, but we know little about how these areas will change over the next 50-100 years. Our study examined the effects of sea-level rise on nine tidal marshes in Washington and Oregon, with the goal of providing scientific data to support future coastal planning and conservation. We compiled physical and biological data, including coastal topography, tidal inundation, vegetation structure, and current and historic sediment accretion rates to assess and model how sea-level rise may alter these ecosystems in the future. Multiple factors, including initial elevation, marsh productivity, sediment availability, and rates of sea-level rise affected marsh persistence. Under a low sea-level rise scenario, all marshes remained vegetated with little change in the present configuration of marsh plant communities or gradually increased proportions of mid, high, or transition marsh vegetation zones. However at most sites, mid sea-level rise projections led to loss of middle and high marsh and gain of low marsh habitat. Under a high sea-level rise scenario, marshes at most sites eventually converted to intertidal mudflats. Two sites (Grays Harbor, and Willapa) appeared to have the most resilience to a high sea-level rise rate, persisting as low marsh until at least 2110. Our main model finding is that most tidal marsh study sites have resiliency to sea-level rise over the next 50-70 years, but that sea-level rise will eventually outpace marsh accretion and drown most high and mid marsh habitats by 2110.
