COUNTRYSIDE COUNCIL FOR WALES
SITE OF SPECIAL SCIENTIFIC INTEREST: CITATION
ANGLESEY CORS ERDDREINIOG
National Grid Reference: SH470820
Site area: 289 ha
Cors Erddreiniog is a large calcareous valley mire of national
importance. There are three fen basins interconnected by the drainage system. A
Carboniferous limestone escarpment, bearing limestone grassland and a hazel
woodland, lies along the eastern side of the main basin. From its foot emerge
base-rich springs, associated with which is a rich flora of black bog rush Schoenus
nigricans; narrow-leaved marsh orchid Dactylorchis traunsteineri,
which has been the subject of taxonomic research; fly orchid Ophrys
insectifera - here growing in a most unusual habitat; and columbine Aquilegia
vulgaris. This orchid-rich vegetation type, found at a few sites in
Anglesey and Lleyn, is not found elsewhere in Great Britain.
Fen dominants include great fen-sedge Cladium mariscus and
blunt-flowered rush Juncus subnodulosus; purple moor grass Molinia
caerulea is spreading in response to aeration following drainage. Locally
there are acidic nucleii with bogmoss Sphagnum spp and
cross-leaved heath Erica tetralix. On the ridge between the central and
NW fen basins is an acidic heathland with marsh gentian Gentiana
penumonanthe in abundance. The site also has a rich insect fauna,
particularly of Lepidoptera and Odonata.
part of the site as a NNR.