Plant Endemism of the Balkan High-Mountain Fens: a Community-Level Synthesis and Their Climate Change Perspective.

The phenomenon of Balkan high-mountain fen plant endemism, unique within Europe, remains poorly studied. We compiled an original dataset of wetland vegetation-plot data across nine countries where Balkan endemics and subendemics occur. We tested the diversity patterns for endemics, non-endemic habitat specialists of bryophytes and vascular plants and matrix-derived taxa with respect to climate, palaeoclimate, edaphic and topographic factors. We used Spearman correlations, Spatial Autoregressive Error Models, Canonical Correspondence Analysis and Principal Component Analysis of abiotic factors with richness patterns projected using Generalised Additive Models. Two major hotspots of fen endemism, centred around the Rila and Korab Mts, were identified. Species composition of endemics generally follows an east-to-west gradient that coincides with palaeoclimatic patterns. Palaeoclimate was influential for community-scale richness of bryophytes and narrow-range endemics, the latter being positively affected by the Bølling-Allerød precipitation peak and the wet-tundra climate during the glacial. The richness of other groups was affected by recent climate, edaphic factors and topography. Water pH differentiated major vegetation types and affected the richness of matrix-derived taxa and fen bryophytes, but had a minor impact on Balkan endemics, except those associated with serpentinite. Several endemic taxa usually co-exist even in small wetland patches. Palaeoclimate shows that fen endemics evidently experienced drier, warmer summers than today over the last 21,000 years; yet they were more affected by past precipitation. If we conserve Balkan high-mountain fens, their catchment properties and hydrology, and maintain moderate grazing, we increase the likelihood that their endemics will withstand ongoing climate change.