Fens, swamps and reedbeds are important wetland communities which can range from rich mosaics with significant marshy grassland components to habitats dominated by single species. In many situations these habitats occur as important part of floodplain grassland sites. A wide range of wetland National Vegetation Community types are represented including S4 common reed (‘reedbed’).  S12 reedmace, S14 branched bur-reed, S6 greater pond sedge, S7 lesser pond sedge and, sometimes (associated with wet woodlands) small areas of S3 greater tussock-sedge.  

 

Fens are wetland sites which depend upon high water levels fed from upwellings and springs or from streams and watercourses. Fens generally occur on more than 0.5 m of peat, often in natural depressions.  There are three main types of fen which are characterised by topographic rather than vegetation ‘criteria’. These are valley mire, basin mire and flood-plain mire. Un-degraded valley and basin mires are now very rare habitats in south Wales, however RCT supports regionally important areas of valley mire. The CCW Phase I survey have identified 110 hectares of lowland valley and basin mire in RCT.  

 

Where drainage is impeded on floodplains, then swamp communities of very wet, often tall emergent wetlands can establish (see also Reedbeds). Characteristic species incudes stands of  pond or bladder sedge (the latter particularly in the Ely Valley), hemlock water dropwort, flag iris and meadowsweet. Only 8 hectares of swamp was recorded in RCT in the CCW Phase I survey. Areas of swamp are genuinely lowland features and occur as small (usually less than 1 ha) sites often in complex mosaics with other wetland habitats. Important sites include Pant Marsh and Coedcae Marsh at Llantrisant, Jubilee Marsh at Llanharan and at Hirwaun Ponds. Fens and swamp are important for their associated flora and as habitat for aquatic invertebrates, amphibians, reptiles and wetland birds. 

 

Reedbeds are specifically areas of wetland dominated by common reed.  Reedbeds support a very specialised and vulnerable flora and fauna, much of which requires large areas of reed. For example, while small reedbeds will support birds such as reed and sedge warbler and wintering water rail, very large reedbeds (over 20 ha) are needed as nesting habitat for bittern and marsh harrier. In RCT there are no reedbeds over 0.25 ha in size. The largest area of reedbed is probably in the lagoons of Cwm Colliery, where a mixed area of common reed occurs with sea club-rush and is large enough to support two or three singing reed warbler. Elsewhere small stands of common reed occur on wetland sites such as Coedcae  Marsh and Pant Marsh (both near Llantrisant) and at the foot of the Gelli Tips in the Rhondda.