Cladium calcareous fen
The calcareous Cladium fens are Community priority habitats under the 92/43/EEC Directive.
These habitats are characterized by the flooding, persistent or temporary, with calcareous groundwaters, calcium-rich but poor in nitrates and phosphates. The Cladium prefers conditions of continuous submersion of their rhizomes, with a level of no more than 30-40 cm.
In these ecological conditions Cladium mariscus is highly competitive, through the land shading and the production of a thick litter of difficult decomposition.
The Cladium fen dealing mainly two types of sites: the first consists of margins of lakes and ponds of adequate hydrological characteristics, which occupy a vegetational strip that fade to the outside with wet meadows and inside with a strip of eliophites as Schoenoplectus lacustris, S. mucronatus, Phragmites australis, Typha latifolia, Sparganium erectum, etc.
The second site consists by fens where the calcareous water surface from underground or slide on surface from sources.
Both the vegetal association are attributed to Cladietum marisci (Zobrist 1933) association.
In the resurgences area the cladium fen intersects with the low Schoenum fen, usually occupying the edges of low-deep pools and low-deep flooded areas in a more or less permanent way. Soil is made up of thin layers of peat (10-40 cm) resting on gravelly or gravelly-silty deposits.
Locally, depending on the characteristics of the site and on the existence of mowing, Cladium may be added by Calamagrostis epigejos, Juncus subnodulosus, Peucedanum marsh, Lythrum salicaria, Mentha aquatic and more rare, Senecio paludosus and Butomus umbellatus.
In less dense areas, on free water surfaces, there are stands of Utricularia minor, U. australis and Chara spp. and mosses Campylium stellatum and Scorpidium scorpioides.
In recent years, the water table lowering and the abandonment of all management activities has caused a considerable loss of diversity in cladium fen. The nutrients increasing caused by the peat mineralization has caused a great increase of Cladium mariscus biomass, which has eliminated most species companions and made to disappear almost entirely small pools.