Does vegetation in restored salt marshes equal naturally developed vegetation

Question: Do low stone dams built to prevent erosion and to restore salt marshes through increased sedimentation affect plant species composition? Location: Dutch Wadden Sea area (ca. 53°N 5°E). Methods: Relevés (N = 170) were made of the vegetation of two restored salt marsh sites on the barrier islands Terschelling (Grië) and Ameland (Neerlands Reid). Existing relevés of salt-marsh vegetation (N = 6198) made along the entire Dutch Wadden Sea coast (both the mainland and the barrier islands) were used as a reference. The vegetation of the two restored sites (Grië NLR data) was compared with the reference by (1) simple species-by-species analysis based on frequencies in both data sets, and by (2) ordination, where relevés of the restored sites were projected into a multivariate space defined by the species' abundances in the reference relevés. Results: Out of the 37 species that are common (i.e. have a frequency >5%) in either the Grië NLR data or the reference data, 31 have frequencies that differ by less than a factor of five, and 23 differ by less than a factor of two. Furthermore, the Grië NLR data occupy a space that is well in the centre of the ordination space defined by the reference data. Conclusions: There are no conspicuous differences between salt-marsh vegetation behind low dams and the vegetation that has naturally developed on unprotected mudflats. We conclude that measures targeting salt marsh development in view of flood protection do not interfere with nature conservation.