A team of scientists partially supported by NOAA NCCOS dug deeper into a dataset of plant species composition spanning 51 marshes over ten years in the San Francisco Bay estuary. Using a systematic modeling approach, the team explored how environmental conditions and species traits influenced plant community variability, scaling up from individual marshes to the entire estuary. The resulting published paper has implications for how scientists and land managers can better predict changes in marsh plant communities in response to sea level rise (SLR) and can guide the development of scale dependent monitoring strategies.
In this study, 81 species were identified across the 51 sites surveyed; however, the number of species observed in any given marsh ranged from 1 to 31, and 10 species made up the majority of observations. Comparisons at the site and estuary scale indicated that species-specific associations with environmental gradients, and the influence of species traits, vary with scale. Species dominance also differed across marsh sites. This context dependence suggests that, in some cases, management approaches to conserving marshes at an individual site should consider regional species diversity and be informed by local-scale processes and monitoring.
While landscape scale marsh models in use today are helpful for predicting where marsh habitat will be under different scenarios of SLR, they aggregate across plant species, often using elevation as a proxy for vegetation, and miss the nuance of how plant functional traits influence marsh processes. Ideally managers working in complex estuaries like San Francisco Bay can strike a balance between managing for the site-specific and estuary-wide conservation of marsh diversity and habitat extent.
For example, by knowing that certain sites have a higher abundance of plant species that are negatively associated with salinity, managers can anticipate greater negative effects of SLR on plant diversity and more closely monitor vegetation composition or associations at these sites as early indicators of change. Meanwhile, across the entire estuary, managers may generally prepare for upland migration of marsh habitat to avoid “coastal squeeze.” Ultimately, impacts at both local and regional scales likely have lasting implications for marsh resilience, ecosystem function (e.g., nutrient cycling), and whether habitat remains for threatened and endangered species.
Citation: Rankin, L.L., Jones, S.F., Janousek, C.N., Buffington, K.J, Takekawa, J.Y., and Thorne, K.M., 2024, Marsh vegetation surveys across the San Francisco Bay Estuary, 2008-2018: U.S. Geological Survey data release, https://doi.org/10.5066/P94F802H.