Calcareous fen

In the UK this habitat is defined by stands of saw sedge (Cladium mariscus) in base-rich fen habitats. The habitat can be species-rich, particularly in stands where the saw sedge struggles to achieve dominance. The habitat is rare in the UK and Wales supports only three sizeable areas: in the Anglesey fens, the Lleyn fens and at Crymlyn Bog on the outskirts of Swansea.

Reference state 1 – Calcareous fen

The richer stands of calcareous fen tend not have any single dominant species and are associated with a range of other fen habitats, particularly transition mires and tall herbs fens. In this image, the vegetation comprises a mix of fen species including saw sedge (Cladium mariscus), common reed (Phragmites australis), tufted sedge (Carex elata) and…

Modified state 1 – Swamp and scrub encroachment

In the past, some of these habitats were kept open by management, such as harvesting of the reeds and sedges for thatch. However, the thatching industry is a niche market now and this practice has ended, enabling increases in the dominance of reeds (Phragmites australis) and tall sedges, such as saw sedge, to pave the…

Modified state 2 – Scrub encroachment

In the absence of management practices, successional processes can lead initially to an increased dominance of reeds and large sedges at the expense of the more open and species-rich areas of transition mire. If there is no management response to this then the next phase of the succession will be a loss of swamp and…