Early seed dynamics and tidal marsh revegetation of a salt pond following tidal reconnection

Abstract

AbstractQuestion(1) Following reconnection, does ground cover in the pond become similar to mature salt marsh sites over time? (2) Do seed densities and species composition of seed banks and seed rain differ between the pond and mature salt marsh, and between elevations? (3) Do seed densities vary over time? (4) Within the pond, can seed densities be explained by the abundance of reproductive plants, elevation, or distance from the pond inlet.LocationDry Creek salt field, South Australia.MethodsWe sampled seed rain (monthly) and seed banks (every three months) 6 to 18 months after tidal reconnection and surveyed ground cover (plant species, logs, seagrass wrack and bare ground) up to 34 months after reconnection. Samples were collected from the pond and from mature marsh vegetation at a reference site, and a site immediately adjacent to the pond inlet.ResultsVegetation cover in the pond increased more quickly at mid elevations compared with low elevations. Regarding the composition of ground cover, seed rain and seed banks, the site became more similar to the adjacent site than to the reference site. Seed densities increased from late autumn to early winter. The pattern of seed densities across sites and elevations differed between seed rain and seed banks. Seeds of Salicornia quinqueflora and Suaeda australis dominated in the pond, reflecting their high seed densities adjacent to the pond inlet. Variation in seed densities of both species in the pond was explained by the abundance of nearby, reproductive conspecifics but not by the distance from the inlet.ConclusionsEarly stages of salt marsh revegetation were driven by tidal import of seeds and by the rapid seed production of early colonising species; however, low seed densities may reduce rates of revegetation at low elevations. Seed dispersal and revegetation may be maximised by undertaking tidal reconnection when seed densities are highest.