Emerging Issues for the Restoration of Tidal Marsh Ecosystems in the Context of Predicted Climate Change

There is currently a large regional effort to restore tidal marsh ecosystems in the San Francisco BayDelta Estuary involving the commitment of hundreds of millions of dollars and broad landscape-scale habitat manipulations. Although climate change has been on the horizon for many years, recent developments suggest that it must be taken seriously as a factor to be considered in future planning for marsh restoration efforts. Tidal marshes are vulnerable to changes in salinity and inundation rates, both of which will be affected by climate change. Restoration sites may be particularly vulnerable given unpredictable sediment inputs and newly established vegetation. Predicted shifts in snowmelt and altered runoff will change estuarine salinity patterns and could have large-scale impacts on marsh dominance, especially for freshwater marshes. Even relatively small salinity changes could lead to shifts in dominant species, with freshwater marshes being replaced by brackish marshes and brackish marshes converted to salt marsh communities. This will cause a reduction in overall estuarine plant diversity and productivity, with possible reverberations for the estuarine food web. Based on monitoring data from San Francisco Bay marshes, we predict that salinity will have a more immediate impact on tidal marsh vegetation than sea-level rise. However, sea-level rise poses a potentially greater long-term threat, depending on its rate, because the effects of inundation and a more persistent salinity regime could cause widespread marsh loss. If ice sheets in Antarctica and Greenland begin melting at rapid rates, inundation impacts could be catastrophic for coastal marshes. Given the magnitude of these potential changes, we urge the restoration and conservation management community to integrate these contingencies into adaptive management process and to join with the broader community in forging more flexible governance institutions that can respond effectively to large-scale uncertainties and trajectories as they unfold.