Origin and contrasting succession pathways of the Western Carpathian calcareous fens revealed by plant and mollusc macrofossils

Calcareous fens are unique environments whose history is almost unexplored. The radiocarbon dates of the basal layers of 49 undisturbed calcareous fens showed that in the Western Carpathians (central Europe) many of the extant fen sites originated fairly recently, with two peaks in the High Middle and Roman Ages, the former corresponding to human-induced changes of the landscape. Conspicuous number of fens also appeared in the Lateglacial and later in the Bronze Age owing to suitable environmental conditions. The Lateglacial calcareous fens were of semi-open character with coniferous trees, a heliophilous understorey, and mollusc communities composed of several snail species typical of glacial landscapes. We found wood of Taxus baccata in six localities between 7390 and 600?cal. a BP, suggesting that calcareous fens could have represented a refugial habitat for this red-listed species during the middle Holocene. Using plant macrofossil and mollusc analyses of three representative profiles we illustrate the most common developmental types: (i) fens originating in the Lateglacial, having an open or semi-open character during the whole Holocene; (ii) open fens originating as wooded wetlands; and (iii) open fens starting their development de novo in the late Holocene. Human activities were responsible for the formation of a high number of calcareous fens, especially in the Outer Western Carpathians, and became important drivers of fen biodiversity development. Only a few recently existing calcareous fens contain old sequences of calcareous deposits. They represent unique natural archives and harbour highly endangered relic populations of fen specialists, making their strict protection urgent.