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