Factors affecting the success of early salt-marsh colonizers: seed availability rather than site suitability and dispersal traits

We evaluated the process of salt-marsh colonization in early successional stages of salt-marsh restoration and investigated how the sequence of species establishment related to different success factors. Vegetation data were collected by permanent plots from the restoration site and adjacent, reference salt marshes during three consecutive periods. Seed length, width and mass were used as dispersal traits, and Ellenberg moisture, salinity and nutrient indices as indicators of site suitability. Seed production in the reference site and seed bank in the restoration site were also investigated. The establishment of salt-marsh species within the restoration site was rapid (less than 5 years). The cover of plant species was not correlated between the restored and the reference sites at the first year of restoration, but this correlation was significant during the following years. Seed availability was more important in explaining the sequence of species establishment than salt and nutrient-limitation tolerance. The first colonizers are known as massive seed producers, with shorter seed length and lower seed mass, which probably increased buoyancy. Among dispersal and site traits, seed length and mass, and in a less extent salinity and nutrients, indicated a relationship with new colonizers. Despite few species have not (yet) appeared in vegetation and seed bank in the restoration site, the existence of an existing salt marsh adjacent to the restoration site is shown to be vital for fast colonization of newly created intertidal areas

Inundation Frequency Determines the Post-Pioneer Successional Pathway in a Newly Created Salt Marsh

The effect of inundation frequency on plant community composition, species turnover, total and growth form cover, species richness, and abundance of individual species was investigated in a newly created salt marsh (Belgium) with a gradient of inundation frequencies from 0.01% to 100%. Cover of all plant species was estimated in 119 permanent 2 × 2 m plots along seven randomly chosen transects perpendicular to the main inundation gradient in 2003, 2005, and 2007. Plant composition change clearly varied along the inundation frequency gradient. The cover of annual species increased at a higher rate at higher inundation frequencies, while cover of perennials increased at higher rate at lower inundation frequencies. Species richness and the abundance of most species increased over time, indicating general absence of competitive exclusion among species. Conversely, the abundance and frequency of Atriplex spp., Chenopodium spp., and Salsola kali strongly decreased over time, indicating their early successional character. Frequent inundations hampered plant species turnover because of the low number of species which can tolerate that environmental condition. The appearance of communities dominated by Elymus athericus or Salicornia procumbens strongly increased over time, leading to a stronger separation of plant communities and an appearance of typical salt-marsh zonation