Welsh Journals

THE LICHENS OF THE GWAUN VALLEY FRANCIS ROSE Though not quite such an exceptional habitat for lichens as Tycanol Wood, the Gwaun Valley in north Pembrokeshire, is rich in corticolous lichens of Oak woods and Sallow carr, including some that are very rare, or even otherwise unknown in S. Wales. In April 1973, the British Lichen Society visited three sites in the Gwaun Valley, and a list is appended of the lichen taxa recorded. Species of major interest include: Parmelia (Cetrelia) cetrarioides, a local oceanic species in W. Britain. Cladonia caespiticia, a species of old trees in old forests. Leptogium cyanescens, a rare hyperoceanic species. Menegazzia terebrata, a species of strongly western distribution in Britain, (though also found in montane forests in central Europe, like Cetrelia cetrarioides): new to South Wales. Ochrolechia inversa, an oceanic species of old woodlands in W. Britain and Brittany: new to South Wales. Opegrapha ochrocheila; Pannaria mediterranea (first detected in Britain in 1968); Parmelia laevigata; Parmelia taylorensis; Parmelia arnoldii, new to Wales; and Tomasellia ischnobela, a species found on Hazel, which until recently was thought to be confined to S.W. Ireland, but is now proving to be widespread, if not common, in S. and W. Britain. The three habitats studied were as follows: (1) Old Oak woodland (high forest), Gallt Pen-rhiw, (SN 063357); (2) Sallow carr S.W. of Llannerch (SN 055350); (3) Llanychlwydog church (SN 012343); churchyard, surrounding trees and woodland. Area (1) is an excellent piece of mature Oak forest with Ash, Hazel, Holly and other trees. To judge from its lichen flora, rich in species of the Lobarion lichen alliance, characteristic of old forests in the W. European lowland areas, it is probably primary woodland, that is, it has probably never been completely cleared, nor converted wholly to coppice without some mature standard trees, as has happened to the bulk of the Gwaun Valley oakwoods at one time or another. Selective felling has however certainly taken place, since there are few very ancient trees present. The lichen species characteristic of the Lobarion in the oak wood include: Catillaria atropurpurea Opegrapha ochrocheila Catillaria sphaeroides Opegrapha rufescens Dimerella lutea Pannaria pityrea Leptogium cyanescens Parmeliella corallinoides Leptogium lichenoides Peltigera horizontalis Lobaria pulmonaria Sticta fuliginosa Nephroma laevigatum Sticta limbata Nephroma parile Sticta sylvatica Area (2) is a wet Swallow carr of the type that probably occupied the wet bottoms in most of the valley woods in S.W. Wales in the past. The oceanic Parmelia laevigata association of very moist, leached acid bark is well developed, as are. Usnea species. The most notable species in the carr