Restoration of salt-marsh vegetation in relation to site suitability, species pool and dispersal traits.
Abstract
Restoration of salt marshes on previously reclaimed land provides an excellent opportunity to study plant colonization and subsequent development of salt-marsh vegetation. Insight into the process of salt-marsh development can guide the design, implementation and evaluation of salt-marsh restoration schemes and help determine appropriate management strategies. We evaluated the process of salt-marsh restoration at a species- and plant-community level and investigated how the sequence of species establishment is related to site suitability, availability of the target species in the local and regional species pools and dispersal traits. It took approximately 5 years for species diversity in the restoration site to become similar to a local reference marsh. The annual species Salicornia spp. and Suaeda maritima colonized and reached maximum abundance first. Perennial species (Puccinellia maritima, Aster tripolium, Spartina anglica, Spergularia media, Atriplex portulacoides and Limonium vulgare) only started to colonize or increase notably in abundance after 3 years of restoration. Plant composition at the highest elevation of the restoration site developed from an annual Salicornia community into a Puccinellia maritima salt marsh, which was similar to the local reference marsh. After 8 years, the lower elevations were still covered by annual Salicornia salt marsh despite the potential for the development of a Puccinellia community. Salt tolerance appeared to be much more important in explaining the sequence of species establishment than the availability of the species in the local or regional species pools or dispersal traits. Synthesis and applications. The prospect of salt-marsh restoration after de-embankment is good, with target species establishing spontaneously and vegetation succession taking place. Because most salt-marsh species are dispersed over short distances, it is important that a well-developed salt marsh is adjacent to the restoration site. The rate of salt-marsh development and species diversity appears to be affected mainly by surface elevation. Proper elevation in relation to tidal inundation is therefore a prerequisite for the successful restoration of salt-marsh vegetation after de-embankment.