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Ecotones as Indicators of Changing Environmental Conditions: Rapid Migration of Salt Marsh–Upland Boundaries

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Abstract

Ecotones, the narrow transition zones between extensive ecological systems, may serve as sensitive indicators of climate change because they harbor species that are often near the limit of their physical and competitive tolerances. We investigated the ecotone between salt marsh and adjacent upland at Elkhorn Slough, an estuary in California, USA. Over a period of 10 years, we monitored movement of the ecotone–upland boundary, plant community structure, and physical factors likely to drive ecotone response. At three undiked sites, the ecotone boundary migrated about 1 m landward, representing a substantial shift for a transition zone that is only a few meters wide. Analysis of potential correlates of this upward migration suggests that it was driven by increased tidal inundation. Mean sea level did not increase during our study, but inundation at high elevations did. While the ecotone boundary responded dynamically to interannual changes in inundation at these undiked sites, the plant community structure of the ecotone remained stable. At two diked sites, we observed contrasting patterns. At one site, the ecotone boundary migrated seaward, while at the other, it showed no consistent trend. Diking appears to eliminate natural sensitivity of the ecotone boundary to interannual variation in oceanic and atmospheric drivers, with local factors (management of water control structures) outweighing regional ones. Our study shows that the marsh–upland ecotone migrated rapidly in response to environmental change while maintaining stable plant community structure. Such resilience, stability, and rapid response time suggest that the marsh–upland ecotone can serve as a sensitive indicator of climate change.

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Acknowledgments

We are grateful to the many people who helped with monitoring fieldwork over these 10 years: M. Bakker, C. Chabre, N. D'Amore, S. Fork, K. Madden, R. Martone, A. Morrow, J. Nicholson, and R. Preisler. J. Haskins and G. Lessa collected and helped to analyze the water level data that were instrumental to our inundation analyses. J. Haskins provided the precipitation data. K. Hayes provided access to a site managed by the Elkhorn Slough Foundation and R. de Bree and R. Stephens allowed us to approach two sites via Elkhorn Ranch. Two anonymous reviewers provided remarkably extensive and constructive feedback that improved the paper. This research was supported by a grant from NOAA's Estuarine Reserve Division to the California Coastal Conservancy and the Elkhorn Slough Foundation on behalf of the Elkhorn Slough National Estuarine Research Reserve, a partnership between NOAA and the California Department of Fish and Game.

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Authors and Affiliations

  1. Elkhorn Slough National Estuarine Research Reserve, 1700 Elkhorn Road, Watsonville, CA, 95076, USA

    Kerstin Wasson, Andrea Woolfolk & Carla Fresquez

  2. Ecology and Evolutionary Biology, University of California, Santa Cruz, CA, 95064, USA

    Kerstin Wasson & Carla Fresquez

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  1. Kerstin Wasson
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  2. Andrea Woolfolk
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  3. Carla Fresquez
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Correspondence to Kerstin Wasson.

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Wasson, K., Woolfolk, A. & Fresquez, C. Ecotones as Indicators of Changing Environmental Conditions: Rapid Migration of Salt Marsh–Upland Boundaries. Estuaries and Coasts 36, 654–664 (2013). https://doi.org/10.1007/s12237-013-9601-8

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  • DOI: https://doi.org/10.1007/s12237-013-9601-8

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