Seed-bank and vegetation development in a created tidal freshwater wetland on the Delaware River, Trenton, New Jersey, USA

The initial stages of seed-bank and vegetation development were documented in a newly created tidal freshwater wetland where donor soils were not applied. The 32.3-ha site adjacent to the Delaware River in New Jersey, USA was completed in stages from November 1993 to November 1994. Objectives of the study were to determine characteristics of the seed bank and vegetation and to monitor spatial and temporal changes. The study was carried out from 1995 to 1999 using three sites (North, East, and South Marshes) and three elevation locations (1 m from a tidal channel, midpoint, and 1 m from the upland edge). Development of the seed bank and vegetation demonstrated tremendous colonization potential derived from regional and local sources. Colonization and complete plant cover occurred within one year, and subsequent changes were rapid. Individual species behaved uniquely regarding colonization time, duration, and decline in both the seed bank and vegetation. Large seed banks of some species were present even after decline in the vegetation. Overall, the seed bank was large, small-seeded and persistent, and diverse. A total of 177 species occurred in soil seed bank and 92 in field vegetation samples, with 72 contributing to cover. Seed-bank densities (mean +/- SE/m(2)) ranged from 450 +/- 152 to 394,600 +/- 29,950. Species richness (species/ sainple) ranged from 3.3 +/- 1.2 to 32.3 +/- 1.8. Density and species richness were clearly reduced by inundation and were lowest in channel edge samples and in the first year (1995). Cover species richness ranged from 1.6 +/- 0.2 to 7.3 +/- 0.6 per quadrat. Complexity of the vegetation increased over time, with lowest diversity along the channels. The 1995 site differences, with greatest densities and species richness in the East Marsh, could be related to site history (timing of construction). Species similarity between the seed bank and vegetation ranged from 11 to 53 % and showed no site, location, or temporal pattern. However, similarity between sites of the seed bank and vegetation increased from 1995 to 1998. Several New Jersey State rare or threatened species, as well as invasive species, were present. Results indicated that it is ecologically feasible to create a wetland adjacent to a tidal freshwater river without use of donor soil and that transplantation had not been necessary.