Restoration of a salt marsh system: temporal change of plant species diversity and composition

Salt marsh grassland along the coasts of the Baltic sea in Germany is the result of several hundred years of agricultural activities, which replaced reeds of the brackish water zone gradually by grazing-resistent salt marsh plants. However, after diking and intensified agricultural landuse salt marsh grasslands along the Baltic Sea are very rare and most plant species in these areas are endangered. We report on a pilot project on a 350 ha area near Greifswald at the coast of the Greifswalder Bodden (Baltic sea). In this area, natural periodic flooding was re-introduced after the opening of the front dike line in 1993. Vegetation changes were recorded from 1994 to 1998, and were analyzed for changes in plant species diversity and composition. We established transects and permanent plots to monitor vegetational changes over five years. For three salt marsh species, Aster tripolium, Inula britannica and Puccinellia distans, number and size of populations were evaluated on the total area of 350 ha. Our analyses illustrate that the re-introduction of natural flooding, in combination with a traditional grazing regime, increases mean species diversity by a factor of four and total species diversity by a factor of 2.4. Five years after removing the dike line nearly 75% of the 350 ha were covered by typical salt marsh and salt grassland vegetation types, which also included 8.0% cover by pioneer vegetation. The three monitored salt marsh species had increased in number and size of colonised patches. We conclude that the restoration of formerly wide-spread salt marsh grassland is possible on a large scale.