Coedydd y Garn

Also within

Dyfed County

Geology & landscape

Geological Feature: Rock Outcrop · Geological Period: Carboniferous · Rock Type: Carboniferous Limestone, Limestone

Birds & fish recorded

Birds

Description

Description On the narrow outcrop of Carboniferous Limestone which surrounds the South Wales Coalfield a distinctive climax woodland, with a rich and varied ground flora, has developed. Such woodland is typically dominated by ash Fraxinus excelsior, with an admixture of wych elm Ulmus glabra, oak Quercus sp, sycamore Acer pseudoplanatus, crab apple Malus sylvestris subsp sylvestris and wild cherry Prunus avium. A well developed shrub layer exists with much hazel Corylus avellana, blackthorn Prunus spinosa and hawthorn Crataegus monogyna, together with the uncommon buckthorn Rhamnus cathartica and spindle Euonymus europaeus. Coedydd y Garn is an outstanding example of this limestone woodland. Along the main ridge, the woods occupy linear tors of limestone. The ground flora includes colourful vernal dominants such as wood anemone Anemone nemorosa, early dog-violet Viola reichenbachiana, lesser celandine Ficaria verna and early-purple orchid Orchis mascula. Areas with a more blocky, pavement-like outcrop are characterized by dog's mercury Mercurialis perennis, soft shield-fern Polystichum setiferum, hart's-tongue Asplenium scolopendrium and bryophyte mats. The uncommon toothwort Lathraea squamaria (a parasitic plant associated with hazel) also occurs here. Dry, exposed outcrops have an interesting flora which includes dwarf spurge Euphorbia exigua, wild thyme Thymus praecox, and wild basil Clinopodium vulgare. In such areas an assemblage of terrestrial molluscs that mostly require dry, calcareous conditions is to be found, typified by Xeroplexa intersecta and the small species, Vallonia excentrica and Cecilioides acicula, the latter most often encountered in nests of ants Lasius spp. The north-facing slopes of Coedydd y Garn include wet, flushed areas dominated by alder Alnus glutinosa and pedunculate oak Quercus robur, in addition to ash. Whilst some of the flushes that emanate from the limestone are predictably calcareous, others are more acidic, being derived from surface waters that pass through humus layers. Throughout much of Coedydd y Garn the abundance of dead wood and the large areas of sunny wood-edge make the site ideal for a varied invertebrate fauna. Uncommon species include the bee chafer Trichius fasciatus (a scarabaeid beetle that mimics bees); glow worm Lampyris noctiluca (whose larvae depend on high mollusc densities) and, in the grassy clearing, the impressive brown and yellow robber-fly Asilus crabroniformis, a rare and endangered asilid which is predatory on other flies. Complementing these rare insects are other uncommon species such as the hoverflies, Arctophila fulva, Platycheirus ciliger, Leucozona laternaria and Portevinia maculata and the marbled white Melanargia galathea and brimstone Gonepteryx rhamni butterflies. A wide variety of woodland birds occur at this site, including nesting pied flycatchers and redstart.

Species mentioned