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Background: In fens, plant species composition is predominantly controlled by two environmental factors: root anoxia and low nutrient availability. Aims: We asked how these filters were reflected to the functional structure of plant communities in natural and drained rich fens. Methods: We analysed traits related to species response to anoxia and nutrient availability, using single-trait and multi-trait approaches in fens of a river valley (Biebrza, Poland). We evaluated results concerning multi-trait indices using a null model consisting of simulated communities. Results: Mycorrhizal status and specific leaf area (SLA) clearly distinguished the communities with different levels of anoxia and nutrient deficiency. Mean values, ranges and variance of canopy height showed the differences in the distribution of plant heights among analysed communities. Conclusions: Functional traits distinguish plant communities of the most endangered mesotrophic fens from eutrophic and drained fens. We highlight the role of nutrient and oxygen deficiency in the assembly of fen vegetation and show the impact of the altered environment on the composition of communities in degraded habitats. We demonstrate that single-trait indices are suitable for identifying of environmental filtering in different types of fen communities. We suggest that caution is justified when using multi-trait indices to assess vegetation patterns.

Although conservation of percolation mires is very important for the European biodiversity, our understanding of their functioning is still insufficient, as most of the studied sites are to some extent degraded. We present a study on the relationship between vegetation patterns, hydrochemical gradients and water level fluctuations carried out in the Rospuda valley (NE Poland), which was recently discovered for science as a uniquely preserved fully functioning percolation mire. Vegetation composition, mire water chemistry and water level dynamics were studied along five transects perpendicular to the valley. Eight major vegetation types were identified: brown moss-small and slender sedge fens, Sphagnum-small sedge fens, brown moss-tall sedge fens, tall sedge-reed fens, pine-birch fen woodlands and shrublands, spruce fen woodlands, inundated alder woodlands, alder spring fen woodlands. The seasonal dynamics of water table was revealed as the major factor explaining vegetation patterns. The studied chemical parameters were relatively homogeneous in the whole mire—there is a rather uniform type of mineral-rich nutrient-poor subsurface water all across the fen.

The research subject is the differentiation of plant communities and the preservation status of wet meadows of the Calthion palustris alliance at sites included in subsidy packages 4 and 5 of the agri-environmental scheme. The habitat was studied on 697 agri-environmental plots located in different areas of Poland. The obtained results show high differentiation of the plant communities, which could be considered as representative of the Calthion palustris alliance meadows in Poland. Disturbances in the habitat conditions were observed on most of the plots and they included: disappearance of characteristic species of the Calthion palustris alliance, encroachment of native, expansive species as well as desiccation of the habitat and the associated eutrophication, caused mostly by unidirectional land drainage systems. The study also attempted to determine the conservation prospects of the habitat considering measures implemented under the agri-environmental scheme.