Cyngor Cefn Gwlad Cymru Countryside Council for Wales
Total Page：16
File Type：pdf, Size：1020Kb
CYNGOR CEFN GWLAD CYMRU COUNTRYSIDE COUNCIL FOR WALES SITE OF SPECIAL SCIENTIFIC INTEREST CITATION FLINTSHIRE/DENBIGHSHIRE ALYN VALLEY WOODS AND ALYN GORGE CAVES Date of Notification : 1957, 1972, 1984, 2002 National Grid Reference : SJ 189640 O.S. Maps : 1:50,000 Sheet number: 116, 117 1:25,000 Sheet number: SJ 16 NE; SJ 16 SE; SJ 26 SW Site Area : 190.3 ha Description : The site is of special interest for its geomorphology, the Alyn Gorge Caves and its semi-natural broadleaved woodlands including their size and specific types of woodland vegetation, its calcareous and mesotrophic grasslands, its scarce plant assemblage, its population of wayfaring tree Viburnum lantana and its population of the grizzled skipper butterfly. Alyn Valley Woods and Alyn Gorge Caves SSSI is located 4km west and north-west of Mold. The site predominantly occupies the steep Carboniferous Limestone escarpment alongside the Afon Alyn between Loggerheads and Rhydymwyn but also includes the subsidiary wooded valleys of the Aber Eilun and Nant Gain to its west. The soils are predominantly well-drained, loamy and often very shallow with locally limestone pavement and much more commonly exposed limestone rock throughout the site. However, the soils in part are derived from the former extensive mining of lead/zinc ores, which have occurred along the Afon Alyn and the working of other minerals such as limestone and calcite. In the flatter valley bottoms, adjacent to watercourses, there are areas of alluvium. The altitude ranges from 115 – 275 m. Geology: Alyn Gorge Caves GCR site comprises three cave systems: Ogof Hesp Alyn, Ogof Hen Ffynhonau and Ogof Nadolig. Ogof Hesp Alyn and Ogof Hen Ffynhonau lie behind resurgences in the Alyn Gorge, and both represent relatively recent phases in the development of the gorge. Many of the cave passages were drained as a result of local mining activities, and now provide excellent examples of both shallow and deep phreatic drainage systems within the limestone. Ogof Hesp Alyn represents a deeper trunk channel which developed within a phreas, fed mainly by input from swallow holes in the surface river. Ogof Hen Ffynhonau is a shallower phreatic conduit with evidence of greater maturity and now lying partly in the vadose zone as existed prior to mine drainage. It contains the best calcite decorations of the three caves. In both systems, cave morphology is unusually well preserved, and the effects of rock type and geological structure on cave development are clearly demonstrated. A smaller cave system, Ogof Nadolig, lies on the northern flank of the gorge and has a variety of calcite decoration and some of its passages display scalloping, the results of solution in fast-flowing water. Collectively, the cave systems contain an impressive range of solutional and erosional features along with extensive sediment sequences characteristic of a range of water-flow regimes and climatic conditions. They provide an important three-dimensional example of underground landform development. Biology: The site supports a large stand of semi-natural broadleaved woodland, extending to over 140 hectares, along the steep valleys of the Afon Alyn and its tributaries, the Nant Gain and Aber Eilun. Parts of the site have been exploited historically for the areas rich mineral resources including limestone, spar/calcite and lead/zinc. The drier woodland is composed predominantly of sessile oak Quercus petraea and ash Fraxinus excelsior , with sycamore Acer pseudoplatanus , beech Fagus sylvatica , and birch Betula pendula locally prominent, while alder Alnus glutinosa dominates the wetter ground of the narrow floodplain. The shrub layer in the drier broadleaved woodland is typically composed of hazel Corylus avellana and hawthorn Crataegus monogyna with occasional wych elm Ulmus glabra and holly Ilex aquifolium . Yew Taxus baccata occurs locally usually at the northern end. Dog’s mercury Mercurialis perennis , ivy Hedera helix and bramble Rubus fruticosus are locally prominent in the field layer. The nationally scarce stinking hellebore Helleborus foetidus and green-flowered helleborine Epipactis phyllanthes are present together with the locally uncommon toothwort Lathraea squamaria and herb Paris Paris quadrifolia. Spring sandwort Minuartia verna , another nationally scarce plant, occurs on open ground on former spoil heaps associated with mining for lead and zinc whilst the nationally scarce rock stonecrop Sedum forsterianum has been recorded on open limestone cliffs within the woodland. Limestone cliffs are widespread throughout the woodland particularly east and south of the Afon Alyn and may be associated with screes. The wet woodland is dominated by alder with scattered ash, birch and sycamore. Scattered hazel Corylus avellana , grey willow Salix cinerea and rowan Sorbus aucuparia form a sparse shrub layer. The largely grassy field layer also supports wetland species including the locally scarce marsh valerian Valeriana dioica and wood horsetail Equisetum sylvaticum . The site supports a large population of the locally uncommon wayfaring tree Viburnum lantana , which is at its northern limit in western Britain. Areas of species-rich calcicolous grassland of several types occur particularly in and around Loggerheads Country Park including stands of the unusual bloody cranesbill Geraniun sanguineum and lesser meadow-rue Thalictrum minus grassland. Uncommon plants associated with this grassland include frog orchid Coeloglossum viride , fragrant orchid Gymnadenia conopsea and pale St. John’s-wort Hypericum montanum . Species-rich mesotrophic grassland occurs at the northern end of the site. In addition, further habitats are present including secondary limestone grasslands, scrub, bracken and running water including the Afon Alyn which add diversity to the site and provide further opportunities for invertebrates. Small areas of limestone pavement also occur. Associated with the scrub are uncommon shrubs such as purging buckthorn Rhamnus cathartica and spurge laurel Daphne laureola . The site supports an important colony of the nationally scarce grizzled skipper butterfly Pyrgus malvae that is associated with the open grassland and scrub. Other butterflies present include the nationally scarce pearl-bordered fritillary Boloria euphrosyne , only recorded in small numbers recently and white letter hairstreak Satyrium w-album , and the locally rare green hairstreak Callophrys rubi , brown argus Aricia agestis and brimstone Gonepteryx rhamni . The brimstone is a very local butterfly in North East Wales. A number of other nationally scarce invertebrates have also been recorded on the site. The site has been extensively studied for its mycological flora. A large number of species have been recorded including national, regional and local uncommon species. 10 species are on the British Red Data List. This large diversity reflects the variety and continuity of habitats found throughout the site and their management history. Lesser horseshoe bats Rhinolophus hipposideros together with other species of Myotid bats have been recorded from several caves and mines throughout the site. Numbers tend to be small at individual localities. Otters Lutra lutra and water voles Arvicola terrestris have been recorded from the Afon Alyn. The following priority biodiversity species have been recorded including otter L. lutra , brown hare Lepus europaeus , lesser horseshoe bat R. hipposideros , pipistrelle bat Pipistrellus pipistrellus , water vole A. terrestris , song thrush Turdus philomelos , linnet Carduelis cannabina , tree sparrow Passer montanus , bullfinch Pyrrhula pyrrhula and pearl-bordered fritillary B. euphrosyne . Remarks Part of the site is classified as the Alyn Valley Woods/ Coedwigoedd Dyffryn Alun candidate Special Area of Conservation. Parts of the site are within the Clwydian Range Area of Outstanding Natural Beauty and Loggerheads Country Park. All bat species including the lesser horseshoe bat Rhinolophus hipposideros and otter Lutra lutra are listed on Schedule 5 of the Wildlife and Countryside Act 1981 (as amended) and Annex II of the EC Habitats Directive (Directive 92/43/EEC on the Conservation of Natural Habitats and of Wild Fauna and Flora). The otter L. lutra , brown hare L. europaeus , lesser horseshoe bat R. hipposideros , pipistrelle bat P. pipistrellus , water vole A. terrestris , song thrush T. philomelos , linnet C. cannabina , tree sparrow P. montanus , bullfinch P. pyrrhula and pearl-bordered fritillary B. euphrosyne are listed in the UK’s Biodiversity Action Plan as Priority species. .