Our knowledge of the history of calcareous fens in the Western Carpathians

We review and summarise the results of an ongoing project dealing with the Holocene history of calcareous fens in the Western Carpathians. Calcareous fens in the Inner Western Carpathians harbour a higher number of rare fen specialists than those in the Outer Western Carpathians even though the abiotic conditions are nearly the same. In order to identify the possible causes, we have studied the history of calcareous fens in the Western Carpathians using multi-proxy analyses including pollen, macrofossils of bryophytes, vascular plants and molluscs and radiocarbon dating. So far, we have dated the basal layers of 72 calcareous fens, 50 of which we have also analysed for biotic proxies. In addition, we analysed 12 profiles in detail to trace their Late Glacial and Holocene history. Most the of analysed calcareous fens are relatively young and originated largely in the Middle Ages and particularly after the Wallachian colonisation. The old fens are mainly located in the Inner Western Carpathians, where we reconstructed various succession pathways. Most of these fens contained open-fen plant and snail communities in the Late Glacial and Early Holocene, but were encroached by alder and spruce carrs in the Middle Holocene. Small open fen patches could probably persist during these forest phases, but we have documented them only rarely — in one case by means of plant macrofossils, and in another one htrough fossil mollusc shells. Only two of the studied calcareous fens (one in a lowland, the other in an inter-mountain basin) were sufficiently documented to be completely open throughout the Holocene, suggesting continuous persistence of fen communities. In one case, we revealed a unique case of reversed succession from an early-Holocene Sphagnum fuscum bog to a late-Holocene calcareous fen. Further, we recorded a number of rare calcareous-fen specialists in old fen deposits. We discuss the possibility of their persistence over the Holocene forest optimum. More profiles need to be analysed to obtain more detailed information on the historical distribution of particular fen species and possibilities of their surviving the Middle Holocene.