Vegetation of temperate inland salt marshes on their north-western border (North German Plain)

Temperate inland salt marshes, formerly used as meadows or pastures, are priority habitats in Europe and are threatened by intensifying anthropogenic activities. They are particularly important because of their biogeographical location on the North German Plain, which is the westernmost hotspot of continental halophytic vegetation in Eurasia. In spite of their remarkably long history of floristic research, there are disproportionately few studies dealing with plant communities. They are traditionally included in the Puccinellion maritimae and Armerion maritimae alliances with a typical distribution along the North and Baltic Sea coasts. The similarity with other inland salt marshes has been overlooked. We surveyed natural and secondary sites with euhalophytic vegetation in central Germany (Saxony-Anhalt and Thuringia) in 2018 and 2020 and analysed 105 phytosociological relevés. This resulted in the identification of three main groups (alliances) containing seven associations: annual hypersaline succulent communities of the alliance Therosalicornion (Salicornietum europaeae, Halimioni pedunculatae-Puccinellietum distantis, Suaedetum maritimae), wet saline meadows of the alliance Juncion gerardi (Triglochino maritimae-Glaucetum maritimae, Scorzonero parviflorae-Juncetum gerardi variant with Glaux maritima) and saline short-grass swards of the alliance Puccinellion limosae (Puccinellietum limosae, Atriplex prostrata community). For each association we defined the typical species composition and calculated Ellenberg indicator values depending on the ecological gradients of soil salinity, nutrients and moisture. To determine possible floristic similarities between the inland and coastal salt marshes, we compared our data with data from other areas of saline vegetation: the southern Baltic Sea coast, Kujawy (Poland), Pannonian Basin (Hungary) and Transylvanian Basin (Romania). We concluded that the salt marshes in inland Germany showed a stronger relation with salt marshes of the remote Pannonian and Transylvanian Basins, and they were well separated from the Baltic salt marshes. Thus, we suggest including inland salt marshes on the North German Plain into the syntaxonomical class of continental halophytic vegetation of Festuco-Puccinellietea.