Estuarine Vegetation at Rush Ranch Open Space Preserve, San Francisco Bay National Estuarine Research

Abstract

The Rush Ranch Open Space Preserve (Rush Ranch) is located at the northwestern edge of the Potrero Hills and includes the largest remaining undiked tidal wetland within the Suisun Marsh region of the San Francisco Estuary. The brackish tidal wetlands grade into the transitional vegetation and undeveloped grasslands of the Potrero Hills, and we describe diverse vegetation that reflects the estuarine position, land use history, and hydrogeomorphic complexity of the site. We present a useful framework for future study of vegetation at this San Francisco Bay National Estuarine Research Reserve site. Rush Ranch includes four major estuarine geomorphic units that are widely distributed in the region and support vegetation: subtidal channel beds, fringing tidal marsh, tidal marsh plain and tidal marsh–terrestrial ecotone. These are distinguished by small variations in hydrology and elevation, as noted and described through field observations and historic vegetation-mapping data. We discuss vegetation within each of these landforms, considering each vegetation community as a function of changing physical environment and biological interactions. Past land use and exotic plant species invasions have substantially altered Rush Ranch's tidal marsh vegetation patterns. Our results indicate 27% of the current estuarine wetland-associated flora at Rush Ranch are exotic species, and several are highly invasive. Despite these influences, Rush Ranch’s position in the landscape provides important and increasingly rare habitat linkages between the tidal marsh and upland grasslands, which allows great potential for restoration and enhancement. We present a detailed flora and vegetation analysis by hydrogeomorphic setting to provide an ecological framework for future monitoring, research, and adaptive conservation management at Rush Ranch.