Prioritizing tidal marsh conservation and restoration efforts given high uncertainty due to future environmental change

Background/Question/Methods

The large uncertainty surrounding the effects of sea-level rise and climate change on tidal marsh habitats and the species that depend on them exacerbates the difficulty in planning effective conservation and restoration efforts. To help conservation practitioners address these effects, we modeled the distribution and abundance of tidal marsh bird species in the San Francisco Estuary every twenty years between 2010 and 2110 in relation to projected changes in sea-level rise, salinity, and sediment availability. These distributions were projected for four future scenarios with assumptions of low or high suspended sediment concentrations and low or high rates of sea-level rise (0.52 m or 1.65 m/100 yr) to assess the sensitivity of models to uncertainty in future conditions. We used the projections of bird populations to develop spatial priorities for conservation and restoration using Zonation conservation planning software.  We explicitly incorporated between-scenario uncertainties into our future prioritization and tested whether spatial priorities changed when we included just current or both current and future tidal marsh bird distribution projections. 

Results/Conclusions

We project overall tidal marsh bird population declines from current levels due to the conversion of high and mid-marsh habitat to low-marsh and mudflats and changes in spring and summer salinity. High sea-level rise scenarios had the biggest impact on bird populations, although the effects were muted under high sediment availability scenarios. There was considerable variation in bird population projections among the four future scenarios we tested and the uncertainty tended to increase from 2030 to 2110. We found substantial differences in our spatial prioritization depending on whether future distributions were included, indicating that effective conservation and restoration management will need to consider the effects of climate change. Our results demonstrate how uncertainty due to future climate change can be explicitly incorporated into conservation planning efforts by prioritizing sites with high quality habitat and low uncertainty in future projections. To demonstrate how our results can be used to support management decisions, we identified important locations in which restoration by breaching levees would most effectively provide long term benefits to tidal marsh bird populations. We used the results from our study to develop a decision support tool where interactive maps of the results can be viewed, queried and downloaded at www.prbo.org/sfbayslr.