Communities of calcareous wet dune slacks dominated by Calamagrostis epigejos, in particular, Calamagrostis epigejos-dominated facies and evolution stages of the Juncus subnodulosus formations of unit E3.418, characteristic of northern French and Belgian dunes and rare fen formations of the Dutch North Sea Islands formed by Carex hartmanii, Calamagrostis epigejos, Carex trinervis, Ophioglossum vulgatum, Salix repens, evolution stage with light sand covering of the fen communities of unit D4.1H.