Chwareli a Glaswelltir Degannwy

Site of Special Scientific Interest · 53.2949, -3.8252

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Clwyd County

Climate exposure

This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.

Coastal

Coastal habitats are exposed to sea-level rise and storm erosion. Where hard sea defences sit behind them, there's nowhere landward to retreat to — a squeeze that keeps compressing the habitat no matter how well it's managed.

Habitats

Bracken scrub, Mixed scrub, Montane scrub

Geology & landscape

Mining / Industrial: Quarry · Geological Period: Cambrian, Ordovician · Rock Type: Mudstone, Sandstone

Landscape processes: Coastal, Glacial, Volcanic / Igneous

Description

Description Chwareli a Glaswelltir Degannwy is of special interest for its geological and biological features: exposures of fossiliferous late Ordovician mudstone and sandstone rocks, maiden pink Dianthus deltoides, small-leaved sweet briar Rosa agrestis and a rare vascular plant assemblage. The site occupies a hillside and series of small disused quarries overlooking the village of Deganwy on the right bank of the Conwy Estuary. The underlying bedrock is late Ordovician mudstones and sandstones with volcanic rocks along the summit of the hill. On the hillside the soils are very sandy and free-draining as they are derived from wind-blown sand (loess). Within the quarried areas soils are derived from quarry spoil. The altitude of the site is between 30 and 80 metres above mean sea level. The quarries at Deganwy are nationally important for providing evidence of a late Ordovician glacio-eustatic fall in sea level. The Hirnantian glaciation caused a major global change in sea level and here the quarrying has exposed the Deganwy Mudstone Formation and the Conway Castle Grit Formation that record the resultant rapidly changing sedimentary patterns in parts of the Welsh Basin. This site includes the type locality of the Deganwy Mudstone Formation of latest Rawtheyan or early Hirnantian age and represents deep-water sediments. The deposition of the overlying Hirnantian age Conway Castle Grits marks a significant change in facies and the Grits are interpreted as slope-base channel-fill deposits that developed as coarse sediments were carried into the Welsh Basin by high-energy debris flows, forming submarine fans. The Conway Castle Grits contain three main facies representing different parts of the submarine fans, with much of the sediment having been transported by turbidity currents. The abrupt change from muds into coarser Hirnantian-age rocks suggests that the glaciation was established very rapidly. The fossil evidence is diverse and clearly allochthonous having been washed-in from shallower water and is important for correlation with Hirnantia fauna elsewhere the UK. The hillside supports a mosaic of grassland, bracken Pteridium aquilinum and gorse Ulex europaeus scrub. The grassland has an open sward with patches of bare ground and is not especially species-rich. The dominant grasses are fescues Festuca spp., bents Agrostis spp. with some coarser species such as cock’s-foot Dactylis glomerata and Yorkshire fog Holcus lanatus. The sandy soil and closeness to the estuary is reflected in the presence of maritime species such as sand sedge Carex arenaria. Herbs present include sheep’s sorrel Rumex acetosella , spring vetch Vicia lathyroides and lady’s bedstraw Galium verum. The upper slopes are lightly grazed by the combined efforts of sheep and rabbits whereas the lower slopes are not grazed by livestock. Several colonies, in total consisting of many hundreds of plants, of the maiden pink are present where there is a light scattering of bracken in the grassland or at the edge of footpaths where these cross through stands of dense bracken. This is the largest known population within the East Gwynedd Area of Search. The small-leaved sweet briar occurs as a thin scattering of bushes on the old spoil banks at the western end of the quarries. Where there are lime-rich soils around the quarry rim and amongst the spoil banks then Nottingham catchfly, spring cinquefoil Potentilla tabernaemontani and other calcicolous grasses such as downy oat grass Avenula pubescens, crested hair-grass Koeleria macrantha, and herbs such as lady’s bedstraw, common rock-rose Helianthemum nummularium, common bird’s-foot trefoil Lotus corniculatus and common restharrow Ononis repens occur in small species-rich patches amongst the bracken and scrub. Remarks The geological feature within the site has been selected as a result of the former Nature Conservancy Council’s Geological Conservation Review, a national survey and evaluation of sites of geological and physiographical interest. The site is described in the GCR volume entitled British Cambrian to Ordovician stratigraphy (Rushton et al., 1999). Maiden pink and Nottingham catchfly are Near Threatened (NT) on both the great Britain (GB) and Wales Vascular Plant Red Data Lists (VPRDL). Small-leaved sweet briar is NT on the GB VPRDL and Critically Endangered (CR) on the Wales VPRDL.

Species mentioned

English name
search for this in other sites		 Latin name
search with Google		 IUCN / Red List Type Family
Phalacrocorax aristotelis Not listed in GB list bird phalacrocoracidae
bracken Pteridium aquilinum LC fern dennstaedtiaceae
downy oat grass Avenula pubescens LC grass poaceae
cock's foot Dactylis glomerata LC grass poaceae
Yorkshire fog Holcus lanatus LC grass poaceae
crested hair-grass Koeleria macrantha NT grass poaceae
maiden pink Dianthus deltoides NT herb carophyllaceae
lady's bedstraw Galium verum LC herb rubiaceae
rock roses Helianthemum nummularium VU herb cistaceae
birdsfoot trefoil Lotus corniculatus LC herb fabaceae
common rest-harrow Ononis repens VU herb fabaceae
spring cinquefoil Potentilla tabernaemontani Not listed in GB list herb rosaceae
sheep's sorrel Rumex acetosella NT herb polygonaceae
spring vetch Vicia lathyroides VU herb fabaceae
sand sedge Carex arenaria LC sedge cyperaceae
gorse Ulex europaeus LC shrub leguminosae

Plant communities

W20 — Montane scrub

Salix lapponum-Luzula sylvatica scrub

Salix arbuscula, Salix cinerea, Salix lapponum, Salix myrsinites, Salix phylicifolia, Salix reticulata, Empetrum nigrum, Calluna vulgaris, Salix lanata, Vaccinium myrtillus, Vaccinium uliginosum, Carex atrata, Carex bigelowii, Carex binervis, Carex flacca, Luzula multiflora, Luzula sylvatica, Huperzia selago, Selaginella selaginoides, Aulacomnium palustre, Mnium hornum, Philonotis fontana, Plagiomnium undulatum, Rhizomnium punctatum, Dicranum bonjeanii, Dicranum majus, Dicranum scoparium, Fissidens adianthoides, Racomitrium lanuginosum, Calliergonell cuspidatum, Ctenidium molluscum, Hylocomium splendens, Hypnum callichroum, Hypnum cupressiforme, Palustriella commutatum, Plagiothecium denticulatum, Plagiothecium undulatum, Pleurozium schreberi, Ptilium crista-castrensis, Rhytidiadelphus loreus, Rhytidiadelphus squarrosus, Rhytidiadelphus triquetrus, Sanionia uncinata, Scorpidium revolvens, Thuidium tamariscinum, Atrichum undulatum, Polytrichastrum alpinum, Sphagnum capillifolium, Sphagnum fallax, Sphagnum girgensohnii, Sphagnum palustre, Sphagnum russowii, Sphagnum squarrosum, Sphagnum subnitens, Sphagnum teres, Barbilophozia barbata, Chiloscyphus polyanthos, Diplophyllum albicans, Lophocolea bidentata, Plagiochila porelloides, Ptilidium ciliare, Scapania undulata, Cladonia squamosa, Peltigera canina, Angelica sylvestris, Caltha palustris, Hieraclium spp., Saussurea alpina, Solidago virgaurea, Campanula rotundifolia, Succisa pratensis, Valeriana officinalis, Rhodiola rosea, Vaccinium vitis-idaea, Thymus praecox, Epilobium anagallidifolium, Dactylorhiza viridis, Euphrasia officinalis, Rhinanthus minor, Oxalis acetosella, Oxyria digyna, Polygonum viviparum, Rumex acetosa, Anemone nemorosa, Ranunculus acris, Thalictrum alpinum, Alchemilla alpina, Alchemilla glabra, Filipendula ulmaria, Geum rivale, Galium boreale, Galium saxatile, Saxifraga aizoides, Saxifraga hypnoides, Saxifraga oppositifolia, Saxifraga stellaris, Viola riviniana, Agrostis canina, Agrostis capillaris, Anthoxanthum odoratum, Deschampsia cespitosa, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Nardus stricta, Dryopteris dilatata, Phegopteris connectilis

W21 — Hedgerow scrub, Mixed scrub

Crataegus monogyna-Hedera helix scrub

Hedera helix, Salix cinerea, Acer pseudoplatanus, Ilex aquifolium, Betula pendula, Corylus avellana, Fagus sylvatica, Quercus robur, Fraxinus excelsior, Malus sylvestris, Sorbus aria, Taxus baccata, Ulmus glabra, Ulmus procera, Sambucus nigra, Viburnum lantana, Euonymus europaeus, Cornus sanguinea, Juniperus communis, Ligustrum vulgare, Clematis vitalba, Rhamnus cathartica, Crataegus laevigata, Crataegus monogyna, Prunus spinosa, Juncus effusus, Plagiomnium undulatum, Brachythecium rutabulum, Kindbergia praelonga, Rhynchostegium confertum, Tamus communis, Heracleum sphondylium, Torilis japonica, Arum maculatum, Arctium minus, Cirsium arvense, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Stellaria graminea, Stellaria holostea, Stellaria media agg., Calystegia sepium, Mercurialis perennis, Geranium robertianum, Iris foetidissima, Glechoma hederacea, Lamium purpureum, Origanum vulgare, Stachys sylvatica, Teucrium scorodonia, Allium ursinum, Hyacinthoides non-scripta, Circaea lutetiana, Rumex sanguineus, Anemone nemorosa, Ranunculus repens, Fragaria vesca, Geum urbanum, Potentilla sterilis, Poterium sanguisorba, Rosa arvensis, Rosa canina, Rubia peregrina, Rubus fruticosus agg., Galium aparine, Urtica dioica, Viola riviniana, Anisantha sterilis, Arrhenatherum elatius, Brachypodium pinnatum, Brachypodium sylvaticum, Bromopsis erecta, Dactylis glomerata, Elytrigia repens, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris filix-mas

W22 — Hedgerow scrub, Mixed scrub

Prunus spinosa-Rubus fruticosus scrub

Hedera helix, Acer campestre, Corylus avellana, Ulex europaeus, Prunus spinosa, Plagiomnium undulatum, Brachythecium rutabulum, Eurhynchium striatum, Kindbergia praelonga, Thuidium tamariscinum, Atrichum undulatum, Lophocolea bidentata, Achillea millefolium, Cardamine flexuosa, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Silene uniflora, Stellaria media agg., Mercurialis perennis, Geranium robertianum, Stachys sylvatica, Teucrium scorodonia, Hyacinthoides non-scripta, Oxalis acetosella, Digitalis purpurea, Plantago lanceolata, Veronica chamaedrys, Armeria maritima, Rumex acetosa, Filipendula ulmaria, Geum urbanum, Rosa canina, Rubus fruticosus agg., Rubus idaeus, Galium aparine, Urtica dioica, Viola riviniana, Agrostis capillaris, Brachypodium sylvaticum, Dactylis glomerata, Festuca rubra, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris borreri, Dryopteris filix-mas

W25 — Bracken scrub

Pteridium aquilinum-Rubus fruticosus underscrub

Hedera helix, Acer pseudoplatanus, Fagus sylvatica, Quercus robur, Fraxinus excelsior, Sambucus nigra, Ulex europaeus, Crataegus monogyna, Prunus spinosa, Luzula multiflora, Mnium hornum, Brachythecium rutabulum, Kindbergia praelonga, Angelica sylvestris, Conopodium majus, Heracleum sphondylium, Arum maculatum, Cirsium arvense, Lonicera periclymenum, Silene dioica, Stellaria holostea, Mercurialis perennis, Geranium robertianum, Glechoma hederacea, Teucrium scorodonia, Hyacinthoides non-scripta, Chamerion angustifolium, Circaea lutetiana, Digitalis purpurea, Rumex acetosa, Anemone nemorosa, Ficaria verna, Potentilla erecta, Rosa arvensis, Rosa canina, Rubus fruticosus agg., Rubus idaeus, Galium aparine, Galium mollugo sens.lat., Galium saxatile, Urtica dioica, Viola riviniana, Agrostis capillaris, Anthoxanthum odoratum, Arrhenatherum elatius, Dactylis glomerata, Festuca rubra, Holcus lanatus, Holcus mollis, Poa trivialis, Pteridium aquilinum, Dryopteris dilatata, Dryopteris filix-mas