Abundance and diversity of tidal marsh plants along the salinity gradient of the San Francisco Estuary: implications for global change ecology

From 2003 through 2005, tidal marsh plant species diversity and abundance on historically surveyed vegetation transects along the salinity gradient of the San Francisco Estuary were investigated to establish empirical relationships between plant distributions and environmental conditions, and furthermore to examine and predict past and future plant distribution changes. This study suggests that for most species, salinity is the primary control on plant distribution. Thus, ongoing changes in estuarine conditions (increasing sea level and salinity) are resulting in a complex mix of plant distribution changes. On the low marsh, where sediment salinity is similar to that of ambient water, halophytic species are replacing salt-intolerant taxa. However, on marsh plains, where increased tidal flooding is moderating high salinity (concentrated by evaporation), halophytic “high marsh” species are being replaced by salt-intolerant “low marsh” taxa. Thus, future changes in plant distributions will hinge on whether marsh sediment accumulation keeps pace with sea level rise.