A Study of the Seed Bank of a Salt Marsh in Northern San Francisco Bay

Abundance, species composition, and distribution of buried seeds in a San Francisco Bay salt marsh were studied by collecting soil samples in October and February and observing seedling emergence in the greenhouse. Results were compared with existing vegetation patterns and field germination. Average numbers of buried viable seed down to a 5-cm depth were 380/ m2 in October and 700/m2 in February, with field germination averaging 118/m2. Salicornia virginica dominated the seed bank in the greenhouse and in field germination. Most other marsh species were present in the seed bank but numbers of seeds were low. A significant correlation was found between highest species diversity and proximity to channels. The nature of this lowdiversity, low-density seed bank reflects dominance of long-lived perennial species, seed dispersal patterns and selective environmental pressures. SEED BANK RESERVOIRS are often a critical aspect of the dynamics of a particular vegetation. Work on wetland seed banks has shown a variety of responses depending upon the location andtype of environment. Prairieglacial marshes experience long-term variability in hydrologic conditions and their regeneration following drawdown depends upon the persistent nature of their seed banks (van der Valk and Davis, 1976, 1978). On the other hand, freshwater tidal marshes in New Jersey, which experience diurnal fluctuations in water level but long-term relative stability, exhibit a seed bank in which most species germinate in early spring when the soil begins to warm (Leck and Graveline, 1979; Parker and Leck, in press; Leck and Simpson, pers. commun.). Few studies have been conducted on salt marsh seed banks. Milton (1939) collected soil cores along the riverbank of an estuary in Wales and found that the dominant species, Glyceria maritima, Juncus maritimus, and Festuca rubra, had very few viable seeds in the soil while other species were well represented in the buried seed flora although scarce in the surface vegetation. He also found that the salt marsh seed bank was dominated by annual species in comparison with low numbers of seeds from perennials. These patterns of lack of correl Received for publication 18 February 1983; revision accepted 15 November 1983. We wish to thank the California Department of Parks and Recreation for permission to work at China Camp State Park and Drs. Michael Josselyn, Curt Davis, and Mary Leck for help with the project and manuscript. 2 Current address: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025. 3 Address reprint requests to V. T. Parker. spondence between seed bank and dominant surface vegetation and of predominance of annuals are also common to many terrestrial studies (Chippindale and Milton, 1934; Oosting and Humphreys, 1940; Major and Pyott, 1966; Livingston and Allessio, 1968). Ungar and Riehl (1980) studied an inland salt marsh in Ohio where the surface vegetation showed distinctly segregated species patterns which were related to soil salinity. Species distributions changed from year to year as soil salinity varied with yearly rainfall patterns. They found seeds from the dominant species of each zone throughout the marsh and concluded that the seed bank provided the potential for changes in vegetation zonation as soil salinity levels changed. The objectives of the present study were to characterize the size, species composition, relative abundance and distribution of the buried seed flora of a well-established salt marsh in San Francisco Bay. California salt marshes have predictable daily and seasonal environmental changes with relatively constant vegetation structure and composition. Our intention was to examine the dynamics of the seed bank in this stressful but relatively stable habitat. The assumption that the species distribution observed along the bay front and along main channel systems can be correlated with patterns of tidal flow was used as an initial hypothesis to detect seed bank distribution patterns and field germination. MATERIALS AND METHODS-This study was conducted at the China Camp State Park salt marsh in Marin County, California (Lat. 38°00'N,Long. 122°30'W).ChinaCampmarsh