Between land and sea – a classification of saline and brackish grasslands of the Baltic Sea coast

Abstract

Aims: Baltic Sea coastal grasslands are influenced by saline or brackish sea water, a narrow tidal range and non-intensive land use. Since their designation as Natura 2000 habitat types under the EU Habitats Directive, they have become an important conservation issue in Europe. Little supra-regional research has been conducted to date on their floristic and ecological diversity, syntaxonomy and geographic variation. We surveyed the geographical distribution and syntaxonomical variation of saline and brackish grasslands to highlight large-scale gradients in species composition, as well as underlying climatic and other abiotic factors. We discuss the resulting vegetation types in the context of northern Europe and review implications for conservation. Study area: Baltic Sea coast. Methods: We compiled a comprehensive plot-based vegetation dataset for the Baltic Sea coast and subsequently selected releves by species composition and plot size. We classified 3,732 releves, using modified TWINSPAN, identified differential species and syntaxa, and performed a DCA with post-hoc fitted intrinsic and climatic variables. We tested main differences in relevant factors for significance. Results: The classification resulted in 33 vegetation types of differing distribution range and area. Most common were the classes Juncetea maritimi and Molinio-Arrhenatheretea, with the classes Phragmito-Magnocaricetea, Cakiletea maritimae, Saginetea maritimae, Scheuchzerio palustris-Caricetea fuscae and Koelerio-Corynephoretea canescentis also present. Baltic Sea coastal grasslands vary in soil salinity and moisture and, to a lesser extent, in nutrient availability and base content. Conclusions: Variation in the plant communities reflects regional phytogeographical patterns. Communities most similar to north-west European coastal grassland types are characterized by euhaline to α-mesohaline site conditions. Designations of the Natura 2000 habitat types H1330 and H1630 require revision. Many Baltic Sea coastal grassland plant communities include species threatened at the national level.