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Salinity thresholds for understory plants in coastal wetlands

Abstract

The effects of sea level rise and coastal saltwater intrusion on wetland plants can extend well above the high-tide line due to drought, hurricanes, and groundwater intrusion. Research has examined how coastal salt marsh plant communities respond to increased flooding and salinity, but more inland coastal systems have received less attention. The aim of this study was to identify whether ground layer plants exhibit threshold responses to salinity exposure. We used two vegetation surveys throughout the Albemarle-Pamlico Peninsula (APP) of North Carolina, USA to assess vegetation in a low elevation landscape (≤ 3.8 m) experiencing high rates of sea level rise (3–4 mm/year). We examined the primary drivers of community composition change using Non-metric Multidimensional Scaling (NMDS) and used Threshold Indicator Taxa Analysis (TITAN) to detect thresholds of compositional change based on indicator taxa, in response to potential indicators of exposure to saltwater (Na, and the Σ Ca + Mg) and elevation. Salinity and elevation explained 64% of the variation in community composition, and we found two salinity thresholds for both soil Na+ (265 and 3843 g Na+/g) and Ca+ + Mg+ (42 and 126 µeq/g) where major changes in community composition occur on the APP. Similar sets of species showed sensitivity to these different metrics of salt exposure. Overall, our results showed that ground layer plants can be used as reliable indicators of salinity thresholds in coastal wetlands. These results can be used for monitoring salt exposure of ecosystems and for identifying areas at risk for undergoing future community shifts.

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Data availability

The data from the peninsula-wide survey are archived and openly available for download via Dryad (https://datadryad.org/) and data from the transect survey are available via Taillie and Poulter (2019) via Pangaea (https://doi.pangaea.de/10.1594/PANGAEA.896941).

Code availability

Code is available on request from the lead author.

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Acknowledgements

The authors would like to sincerely thank the hard work and dedication of Ethan Baruch, Christina Bergemann, Charles Camp, Ashley Green, Sam Mahanes, Matthew Stillwagon, and Anna Wade in data collection in the field and lab. They would also like to thank the members of the Bernhardt lab at Duke University, the Ardon lab at N.C. State University, and Justin T. Mann at Binghamton University for crucial feedback on various editions of this manuscript, Robert Peet and the Carolina Vegetation Survey for access to survey plots, and Bonnie McGill, PhD for plant illustrations in Fig. 4. Sincere thanks to National Science Foundation for funding this research and earlier sources of funding (from a NASA Earth Science Fellowship) that established the plot networks on the Albemarle Peninsula. Additional thanks to the College of Natural Resources at North Carolina State University and Department of the Interior Southeast Climate Adaptation Science Center and for funding data collection efforts for the transect survey.

Funding

National Science Foundation (Coastal SEES Collaborative Research Award Grant No. 1426802, DEB-1713435, and DEB 1713502).

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Authors and Affiliations

Authors

Contributions

JW, EB, CM, and MA procured funding to support this research; SA, JW, EB, and EU conceived the primary research idea; SA, PT, and EU collected field data; SA, BP, and PT selected research sites; SA conducted all analysis and wrote the manuscript with JW; EU generated maps; and all authors discussed results and contributed in edits to manuscript.

Corresponding author

Correspondence to Justin P. Wright.

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The authors declare that they have no conflict of interest.

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Not applicable.

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Nomenclature

A.S. Weakley 2015, Flora of the Southern and Mid-Atlantic States.

Additional information

Communicated by Julie C. Zinnert.

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Anderson, S.M., Ury, E.A., Taillie, P.J. et al. Salinity thresholds for understory plants in coastal wetlands. Plant Ecol 223, 323–337 (2022). https://doi.org/10.1007/s11258-021-01209-2

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  • DOI: https://doi.org/10.1007/s11258-021-01209-2

Keywords

  • Coastal wetlands
  • Saltwater intrusion
  • Vegetation change
  • Community composition
  • Salinity threshold
  • Regime shifts