The seed bank of a freshwater tidal marsh.

Presence of buried viable seeds at three depths in freshwater marsh soils was determined by observing seedling emergence in the greenhouse. These results were compared with field germination. For the greenhouse study soils were collected in December 1976, and March 1977, from six vegetation types in the Hamilton Marshes near Trenton, New Jersey. Three to five times more seeds and almost three times as many species germinated in the greenhouse than in the field. Of the ten most numerous species in greenhouse samples, 7.2 ? 0.2 SE species were also observed as seedlings at that site in the field. Annuals comprised seven of the ten most numerous species in both the greenhouse and in the field. Estimated seed densities for the top 10 cm of marsh soil ranged from 6,405 to 32,400 seeds m-2. Germination in soils collected in March was 3 1% greater than for those collected in December. Decrease in species number with depth was significant for March soils. While seedling numbers also decreased with depth, considerable variability occurred and the differences were not significant. The seed bank profile suggests that viability and/or dormancy are prolonged in these freshwater tidal marsh soils. BURIED seed communities provide clues to the past vegetation (Odum, 1965, 1978) and suggest the course of revegetation and succession following disturbance. Buried seeds are often those of successional species which can take advantage of the "open" habitat which is provided after disturbance (Johnson, 1975). Our understanding of buried seeds comes largely from terrestrial environments, such as agricultural fields (e.g., Brenchley and Warington, 1930, 1933; Schafer and Chilcote, 1970), forests (e.g., Oosting and Humphreys, 1940; Johnson, 1975; Moore and Wein, 1977), and grasslands (e.g., Major and Pyott, 1966). The seeds of marsh soils have received attention only recently (van der Valk and Davis, 1976, 1978) following a long hiatus since the reports of Darwin (1859) and Milton (1939). There have been no studies of the seed banks of freshwater tidal marshes, which unlike saline tidal marshes are often dominated by annual species (Whigham et al., 1978). To develop an even rudimentary understanding of marshland vegetation patterns, species distribution, and reproductive strategy, seed bank composition and viability must be characterized. We use seed bank to refer to the viable seeds found in soil as determined by the appearance of seedlings although we recognize the difficulty inherent in using germinability to establish the ' Received for publication 19 September 1978; revision accepted 5 June 1979. The authors would like to thank R. L. Simpson, D. F. Whigham, V. T. Parker, M. J. Nicolick, and reviewers for discussions and/or suggestions regarding the manuscript, and D. E. Fairbrothers and the Chrysler Herbarium at Rutgers University for aid in identifying certain specimens. The work was supported in part by a grant from Rider College to the senior author. composition and size of the seed bank because germination requirements may not be provided (Major and Pyott, 1966). The germination requirements of aquatic plants are discussed by Hutchinson (1975) and Sculthorpe (1967). Both longevity of seeds and dormancy may be affected by soil moisture levels (Milton, 1939; Champness and Morris, 1948), temperature (Schafer and Chilcote, 1970), and soil atmosphere (Roberts, 1972). The tidal marsh soils are continuously saturated and may provide an ideal environment for maintaining viability. The principal objective of this study was to estimate the size and species composition of seed banks in several vegetation types from a freshwater tidal marsh. Emphasis was placed on seed germination as a function of soil depth. The effects of standing water and intermittent watering on germinability, and the relationship between germination patterns in the field and of seeds in soils removed to the greenhouse were also determined. MATERIALS AND METHODS-A study was made of seed storage in soils from tidal areas of the Hamilton Marshes near Trenton, New Jersey. The Hamilton Marshes cover approximately 500 hectares along an old meander next to the Delaware River (Whigham and Simpson, 1976). Of this area 260 hectares are freshwater tidal marshland, constituting the northernmost tidal marsh in the Delaware River estuary. The climate is temperate, and the growing season lasts from mid-April to late September (avg. temperature 12.1 C). Water supply in the marsh is always adequate. The soils are highly organic (15-50%) silt and silt-clay types (Whigham and Simpson, 1976). Unlike salt marshes, vascular