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Special Areas of Conservation

Corsydd Llŷn/ Lleyn Fens

Designated Special Area of Conservation (SAC)
Country Wales
Unitary Authority West Wales and The Valleys
Centroid* SH313366
Latitude 52.90027778
Longitude -4.509166667
SAC EU Code UK0030187
Status Designated Special Area of Conservation (SAC)
Area (ha) 282.7
* This is the approximate central point of the SAC. In the case of large, linear or composite sites, this may not represent the location where a feature occurs within the SAC.
Location of Corsydd Llŷn/ Lleyn Fens SAC

General site character

  • Inland water bodies (Standing water, Running water) (5%)
  • Bogs, Marshes, Water fringed vegetation, Fens (50%)
  • Improved grassland (30%)
  • Other arable land (5%)
  • Broad-leaved deciduous woodland (10%)

Download the Standard Data Form for this site (PDF <100kb)

Note When undertaking an appropriate assessment of impacts at a site, all features of European importance (both primary and non-primary) need to be considered.

Annex I habitats that are a primary reason for selection of this site

  • 7230 Alkaline fens

    Corsydd Llyn consists of a chain of four rich-fen sites running across the centre of the Lleyn Peninsula, north-west Wales. Cors Geirch is the largest component site and consists of a sinuous valley mire system linking with Cors Edern to the north via a narrow isthmus of modified mire on deep peat; the remaining two component sites of Cors Hirdre and Aber Geirch occupy separate hydrotopographical units close to the north Lleyn coast. The alkaline fen manifests as soligenous communities referable to NVC type M13 Schoenus nigricans – Juncus subnodulosus mire, together with M9 Carex rostrata – Calliergon cuspidatum/giganteum mire in dominantly topogenous settings – stands with elements of both communities are also present. Much of the alkaline fen interest at this site occurs within a matrix of anthropogenically-modified peatland vegetation in which bog myrtle Myrica gale, purple moor-grass Molinia caerulea, blunt-flowered rush Juncus subnodulosus and common reed Phragmites australis occur as prominent components; great fen-sedge Cladium mariscus is also locally dominant. Outstanding floristic features of the alkaline fen at Corsydd Llyn include the nationally rare slender cottongrass Eriophorum gracile at its sole north Wales station, together with significant populations of narrow-leaved marsh orchid Dactylorhiza traunsteineri, grass of parnassus Parnassia palustris and lesser-tussock sedge Carex diandra.

Annex I habitats present as a qualifying feature, but not a primary reason for selection of this site

Annex II species that are a primary reason for selection of this site

  • 1016 Desmoulin's whorl snail Vertigo moulinsiana

    The population of Desmoulin’s whorl snail Vertigo moulinsiana on Cors Geirch NNR occurs in stands of great-fen sedge Cladium mariscus in calcareous fen and is the only locality known for the species in Wales.

Annex II species present as a qualifying feature, but not a primary reason for site selection

Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.