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Variation in tidal wetland plant diversity and composition within and among coastal estuaries: assessing the relative importance of environmental gradients
Citation:
Janousek, Chris AND C. Folger. Variation in tidal wetland plant diversity and composition within and among coastal estuaries: assessing the relative importance of environmental gradients. JOURNAL OF VEGETATION SCIENCE. Opulus Press AB, Uppsala, Sweden, 25(2):534-545, (2014).
Impact/Purpose:
We collected baseline data on coastal wetland plant assemblages in Oregon estuaries to help evaluate potential climate change impacts such as sea-level-rise. Our data suggest that smaller scale features of estuaries such as habitat type and local environmental gradients have a larger effect on plant composition than watershed differences. Common plant species separated more or less into different groups of taxa along soil salinity and elevation gradients. Different plant assemblages generally occupied different National Wetlands Inventory habitat classes, although many common species were found in more than one class. Habitat classes also differed in soil salinity and other soil characteristics. In the course of our work, we documented at least 103 species and 20 assemblages in four coastal estuaries from northern to southern Oregon, highlighting the remarkable diversity of plants these wetlands. Modeling sea-level rise effects on wetland structure and function will be enhanced by incorporating data on the distribution of wetland vegetation along important environmental gradients.
Description:
Question: Does wetland plant composition vary more by estuarine type (differentiated by the degree of riverine versus oceanic influence) or habitat type within estuaries (defined by US National Wetlands Inventory [NWI] marsh classes)? Location: Oregon estuaries: Netarts Bay, Yaquina Bay, Alsea Bay and Coquille River. Methods: We assessed assemblage composition and species cover and richness in 166 plots in tidal marsh and swamp. We also measured canopy density, sediment properties (salinity, grain size, organic matter), and elevation with cm-accuracy GPS. We identified assemblages with cluster analysis and compared spatial patterns of richness and composition with univariate tests, species accumulation curves, nMDS, and CCA. Results: We found substantial cumulative diversity in the tidal wetlands, including at least 103 species and 12 common assemblages. Individual estuaries had similar overall composition and diversity, but the presence, frequency and cover of some species varied by site. Plant composition and edaphic conditions differed more markedly among NWI marsh habitat types. Low marsh had less dense canopies of succulents and grasses and soils with higher salinity and lower organic matter. Palustrine tidal marshes had the lowest soil salinity (though > 0.5 even during winter) and highest organic matter of all three classes, and were very different floristically from low marsh. High marsh plant composition and soil characteristics were generally intermediate between low and palustrine marsh. Assemblages varied in species richness and often occupied different positions along gradients of tidal elevation, soil salinity, and/or sediment particle size. Individual species separated along salinity and elevation gradients. Conclusions: Gradients within estuaries, more so than differences among them, appear to structure plant assemblages in Pacific Northwest tidal wetlands. Estuaries with markedly different degrees of riverine influence supported similar floras, perhaps in part because a wide range of environmental niches were found in all watersheds. Habitat class characterized basic differences in edaphic conditions and overall plant composition reasonably well, but it poorly predicted richness and masked significant small-scale topographic and vegetation complexity.
