Vertical Zonation and Niche Breadth of Tidal Marsh Plants Along the Northeast Pacific Coast
The distribution patterns of sessile organisms in coastal intertidal habitats typically exhibit vertical zonation, but little is known about variability in zonation among sites or species at larger spatial scales. Data on such heterogeneity could inform mechanistic understanding of factors affecting species distributions as well as efforts to assess and manage coastal species and habitat vulnerability to sea-level rise. Using data on the vertical distribution of common plant species at 12 tidal marshes across the US Pacific coast, we examined heterogeneity in patterns of zonation to test whether distributions varied by site, species, or latitude. Interspecific zonation was evident at most sites, but the vertical niches of co-occurring common species often overlapped considerably. The median elevation of most species varied across marshes, with site-specific differences in marsh elevation profiles more important than differences in latitude that reflect regional climate gradients. Some common species consistently inhabited lower or higher elevations relative to other species, but others varied among sites. Vertical niche breadth varied more than twofold among species. These results indicate that zonation varies by both site and species at the regional scale, and highlight the potential importance of local marsh elevation profiles to plant vertical distributions. Furthermore, they suggest that coastal foundation species such as marsh plants may differ in their vulnerability to sea-level rise by being restricted to specific elevation zones or by occurring in narrow vertical niches.
KeywordsRealized niche Salt marsh Sea-level rise Species distribution Tidal datums
We thank K. Powelson, K. Lovett, K. Buffington, L. Curry, C. Freeman, L. Bellevue, M. Holt, and H. Robinson who conducted the extensive vegetation and elevation sampling in the field. We also thank C. Freeman (USGS) for producing Fig 1. and Supplementary Fig.1 and J. Callaway, J. Crooks, and two anonymous reviewers for their helpful comments on the manuscript. The Northwest and Southwest Climate Adaptation Science Centers of the US Department of the Interior funded this study, with additional support from NOAA grant NA15NOS4780171. We thank the following agencies and individuals for site access: US Fish and Wildlife Service (A. Yuen, SDB; E. Nelson, MAD; D. Ledig, COQ; R. Lowe, SIL; G. Nakai, GRA), NOAA’s National Estuarine Research Reserve System (J. Crooks, TIJ; C. Cornu, COO), California State Parks (A. Kitajima, MOR), Marin County Parks (W. Carmen, BOL), California Department of Fish and Wildlife and Orange County Parks (C. Navarro, NEW), Skokomish Indian Tribe (S. Kirby, SKO), and the Nature Conservancy (J. Boyd, STI). Most raw data generated for this study are available as USGS data releases. Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the US government. The US government is authorized to reproduce and distribute reprints of this article for governmental purposes.
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