Ceunant a Thyrrau Trefgarn / Treffgarne Gorge and Tors

Site of Special Scientific Interest · 51.8844, -4.9732

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Dyfed 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, Fast flowing river and stream, Mixed scrub, Montane scrub

Geology & landscape

Geological Feature: Gorge / Ravine · Mining / Industrial: Quarry · Geological Period: Precambrian · Rock Type: Rhyolite

Landscape processes: Coastal, Fluvial, Volcanic / Igneous

Birds & fish recorded

Fish

SpeciesSeason
Bullhead Unknown
River lamprey Unknown

Description

Description Ceunant a Thyrrau Trefgarn/Treffgarne Gorge and Tors SSSI is of special interest for its geomorphology, its range of heathland, grassland and river habitats, and populations of otter Lutra lutra, bullhead Cottus gobio, river lamprey Lampetra fluviatilis and brook lamprey Lampetra planeri. The site is situated approximately 9 km north of Haverfordwest. The deep gorge of the Western Cleddau River, 25m above sea level, bisects the site whilst the highest of the tors reaches an elevation of 156m. GEOLOGY: Treffgarne is an important geomorphological site for the study of tors. It comprises two tors, Poll Carn and Maiden Castle, developed in Precambrian rhyolite, together with adjacent blockslopes and a quarry section showing deeply weathered bedrock overlain by superficial slope deposits. The site, therefore, displays several key elements that have featured in theories of tor formation and provides evidence for a range of geomorphological processes that have shaped the landscape of south-west Wales. BIOLOGY: Flowing through the narrow gorge between great Treffgarne and Little Treffgarne Rocks, the Western Cleddau River supports populations of otter, bullhead, brook lamprey and river lamprey throughout most of its length. The narrow base of the gorge adjacent to the river consists largely of undisturbed scrub and woodland, which provides excellent cover and shelter for the otter. The river itself also supports an aquatic plant community including water crowfoot Ranunculus spp. and water starwort Callitriche spp. vegetation (‘water courses of plain to montane levels with the Ranunculus fluitans and Callitricho-Batrachion vegetation’), a community of European importance. The two tors of Maiden Castle and Poll Carn are distinct features of the Pembrokeshire landscape. The slopes leading to these landmarks support dry heathland of western gorse Ulex gallii and heather Calluna vulgaris which is being increasingly invaded by areas of bracken Pteridium aquilinum. There is a small area of wet heathland comprising mainly deergrass Trichophorum cespitosum and cross-leaved heath Erica tetralix. Large boulders and patches of acidic grassland add further to the diversity. The east-facing slopes of a disused quarry, covered with a mosaic of secondary woodland, scrub and patches of relic heath, form an outlier to the main site. Higher up the gorge, the ungrazed ledges support large patches of great woodrush Luzula sylvatica, sheep’s fescue Festuca ovina and some heather. Scarce plants include Tunbridge filmy-fern Hymenophyllum tunbrigense. Although this species grows on great Treffgarne Rocks and close to Maiden Castle, it is confined to damp sheltered crevices in the shadiest places, where it is certainly a relict of a once more widespread population. Large stands of spring squill Scilla verna are a component of the open bracken and rocky areas. This maritime lily is rarely found far from the coast and its abundance seven miles inland is notable. Climbing corydalis Corydalis claviculata grows around the tors. Over a hundred different mosses and liverworts have been recorded from the gorge and tors, including several western oceanic species of limited distribution in west Wales. These include Scapania gracilis, locally abundant on the north side of great Treffgarne Rocks and Bazzania trilobata locally frequent around Maiden Castle where Lepidoza cupressina is also found on boulders close to the north side. About 50 species of lichen have been recorded, including the locally notable species, Sphaerophorus globosus. The Cladonia heath community, occurring on boulders and amongst heather, is at its richest on Little Treffgarne Rocks. Its value for lower plants was recognized as long ago as 1811, when Richard Fenton described the gorge as “covered with tangled shrubs, lichens and mosses of various sorts and colours”. Two scarce heathland insects with a southern distribution are present: the bugs Alydus calcaratus and Megalonotus dilatatus. The dark bush-cricket, Pholidoptera griseoaptera, also occurs and the keeled skimmer dragonfly, Orthetrum coerulescens, breeds on the floor of the disused quarry. Remarks: Part of Ceunant a Thyrrau Trefgarn/Treffgarne Gorge and Tors SSSI lies within the Afonydd Cleddau / Cleddau Rivers candidate Special Area of Conservation. The following cSAC features are present on this site: water crowfoot and water starwort habitat, otter, bullhead, brook lamprey and river lamprey. Most of the site is registered as common land.

Species mentioned

English name
search for this in other sites		 Latin name
search with Google		 IUCN / Red List Type Family
Megalonotus dilatatus Not listed in GB list bug rhyparochromidae
dark bush-cricket Pholidoptera griseoaptera LC bush cricket tettigoniidae
otter Lutra lutra LC carnivore mustelidae
keeled skimmer Orthetrum coerulescens LC dragonfly libellulidae
Tunrbidge filmy-fern Hymenophyllum tunbrigense VU fern hymenophyllaceae
bracken Pteridium aquilinum LC fern dennstaedtiaceae
bullhead Cottus gobio Not listed in GB list fish cottidae
sheep's fescue Festuca ovina LC grass poaceae
corydalis Corydalis claviculata Not listed in GB list herb fumariaceae
water crowfoots Ranunculus fluitans LC herb ranunculaceae
spring squill Scilla verna LC herb liliaceae
river lamprey Lampetra fluviatilis LC lamprey petromyzontidae
brook lamprey Lampetra planeri LC lamprey petromyzontidae
coral lichen Sphaerophorus globosus LC lichen no common name
greater whipwort Bazzania trilobata LC liverwort jungermanniales
rock fingerwort Lepidoza cupressina Not listed in GB list liverwort jungermanniales
western earwort Scapania gracilis LC liverwort jungermanniales
great wood rush Luzula sylvatica LC rush juncaceae
deergrass, deer sedge Trichophorum cespitosum LC sedge cyperaceae
western gorse Ulex gallii LC shrub leguminosae
bell heather or ling Calluna vulgaris NT shrub dwarf ericaceae
cross leaved heath Erica tetralix NT shrub dwarf ericaceae

Plant communities

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea

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