Formalized classification of the class Montio-Cardaminetea in Europe: towards a consistent typology of spring vegetation

The class Montio-Cardaminetea includes vegetation of springs with constant water flow. These habitats, which function as islands for highly specialized and sensitive biota, are endangered by ongoing landscape and climatic changes. Although a harmonized classification into vegetation units is necessary for effective habitat conservation, there is currently no synthetic classification of the class Montio-Cardaminetea. Here a large set of vegetation-plot records was obtained from national and private databases. The aim was to validate the EuroVegChecklist classification scheme, search for additional ecologically meaningful vegetation types and develop an automatic system for classifying new plots from Europe. We formally defined the cores of eight of the ten EuroVegChecklist alliances: Caricion remotae, Cratoneurion commutati, Lycopodo europaei-Cratoneurion commutati, Epilobio nutantis-Montion, Koenigio-Microjuncion, Mniobryo-Epilobion hornemanii, Philonotidion seriatae (Cardamino-Montion) and Swertio perennis-Anisothecion squarrosi, which were also reproduced by unsupervised classifications. Both unsupervised and semi-supervised classifications further suggested two alliances not previously recognized in the EuroVegChecklist: Anthelion julaceae (liverwort-dominated subalpine to alpine springs in highly oceanic regions in Britain) and Cratoneuro filicini-Calthion laetae (mesotrophic herb-rich subalpine and alpine springs). The unsupervised classifications mainly reflected the base saturation gradient, distinguishing between calcareous and non-calcareous springs. Therefore, it is suggested the order Montio-Cardaminetalia, which is broadly delimited in the EuroVegChecklist, be divided into two separate orders and the following three orders should be distinguished within the class Montio-Cardaminetea: Cardamino-Chrysosplenietalia (non-calcareous forest springs; Caricion remotae), Cardamino-Cratoneuretalia (calcareous springs; Cratoneurion commutati, Lycopodo europaei-Cratoneurion commutati) and Montio-Cardaminetalia (non-calcareous non-forest springs; all other alliances).