Tidal Marsh Vegetation of China Camp, San Pablo Bay, California

Abstract

China Camp (Marin County, California) preserves extensive relict stands of salt marsh vegetation developed on a prehistoric salt marsh platform with a complex sinuous tidal creek network. The low salt marsh along tidal creeks supports extensive native stands of Pacific cordgrass (Spartina foliosa). The outer salt marsh accreted following hydraulic gold mining sedimentation. It consists of a wave-scarped pickleweed-dominated (Sarcocornia pacifica) high salt marsh terrace with a broad fringing low marsh dominated by S. foliosa, including intermittent, variable stands of alkali-bulrush (Bolboschoenus maritimus). Most of the extensive prehistoric salt marsh plains within the tidal creek network also support mixed assemblages of S. pacifica, but high marsh zones along tidal creek banks support nearly continuous linear stands of gumplant (Grindelia stricta) and saltgrass (Distichlis spicata) with more diverse salt marsh forb assemblages. Salt pans with submerged wigeongrass (Ruppia maritima) are scarce, local, and small. The landward edge of the tidal marsh forms rare examples of ecotones with adjacent terrestrial vegetation, including those of alluvial valleys (riparian scrub and woodland, freshwater marsh, sedge-rush meadows) and hillslope grassland and oak woodland vegetation. Narrow high tidal marsh ecotones bordering terrestrial grasslands are locally dominated by creeping wildrye (Elymus triticoides) and Baltic rush (Juncus balticus), mostly on south-facing slopes. Brackish tidal marsh ecotones above ordinary high tides are associated with freshwater discharges from groundwater and surface flows. Brackish marsh ecotones support large clonal stands of sedge, bulrush, and rush vegetation (Carex praegracilis, C. barbarae, Bolboschoenus maritimus, Juncus phaeocephalus, Schoenoplectus acutus), intergrading with terrestrial freshwater wetlands and salt marsh. The terrestrial ecotone assemblages at China Camp are comparable with those of other prehistoric tidal marshes in the San Francisco Estuary, but China Camp lacks most native clonal perennial Asteraceae and halophytic annual forbs of the region’s remnant high tidal marsh ecotones. Few globally rare salt marsh plant populations have been reported from China Camp within the National Estuarine Research Reserve and State Park boundaries, but some species regionally uncommon in San Francisco Bay tidal marshes occur. To date, non-native tidal marsh plant invasions have been relatively minor and localized within China Camp.