Llanelli Naturalists Newsletter - December 1983
Ian Morgan

Cwm Clydach

This is a deep gorge located between Mynydd-y-Garreg and Pont Newydd, the rocks are mostly sandstones, flaggy sandstones and shaley beds of Westphalian age (c. 300 million years old); some of the strata are calcareous and this is attested by the number of plants that are calcioles (i.e. liking lime in the soil) that are to be found. The gorge has been incised into a low ridge that can seen elsewhere around the rim of the South Wales coalfield and because no coal could be found under the rocks represented in this ridge it was nicknamed the 'Farewell Rock" by miners.

The wooded sides of the gorge are dominated by three tree species Oak (Quercus robur), Ash (Fraxinus excelsior) and Wych Elm (Ulmus glabra); the last two favouring base-rich soils. The pH of the gorge's soil varies; towards Mynydd-y-Garreg it gets more acid and this is reflected by the plants found.

In the gorge itself, humidity levels are high and Bryophytes (mosses and liverworts) and ferns are abundant. These non-flowering plants all require damp conditions at least at some stage of their life-histories. The mosses and liverworts have been surveyed by Doctors R.Y. Stringer and Dic Davies, at least 34 species have been recorded and these include so called "Atlantic" species, i.e. those whose distributions in Europe are limited to the maritime peripheries of the west where moisture levels are high and winters relatively mild. One such species is Hookeria lucens, a beautiful moss with large, translucent leaves and one of the few British representatives of a mainly tropical family; exposure to direct sunlight kills it. Mosses and liverworts attain a luxuriance seldom seen in most local woodlands; there is plenty of scope to give the Bryologist ample to research.

Ferns, too, are a prominent feature of this narrow cwm. The calcareous nature of soils results in an abundance of the Soft-shield Fern (Polystichum setiferum) and Hart’s Tongue Fern (Phyllitis scolopendrium). Both are most common in the South-west of Britain, being infrequent or rare in North-east areas.

Also present, even in unusually deep shade is the Maidenhair Spleenwort (Asplenium trichomanes ssp. quadrivalens); it too likes base-rich sites. Male Fern (Dryopteris filix-mas) occurs here and there with Broad-buckler Fern (D. dilatata) frequent in the more acidic patches. The wet flushes commonly hold Lady Fern (Athyrium filix-femina) with hard Fern (Blechnum spicant) on steeper, still wet, areas. Dryopteris affins ssp. affinis Golden-scaled Male Fern occurs.

The hard shield Fern (Polystichum aculeatum) only occurs sparingly and it has hybridized with P. setiferum to form P. x bicknellii at its only known site in Carmarthenshire; it is rare for its parents are usually ecologically separated.

On branches perilously overhanging the ravine is to be seen a type of Polypody fern, Polypodium interjectum (which with the other polypodies could be regarded as our only group of common epiphytic ferns. Epiphytes are plants that grow on trees).

Behind a ruined cottage (beside; the road parallel to Cwm Clydach), Butchers Broom (Ruscus aculeatus) grows; no doubt planted by the past occupiers; it was used by butchers to clean their chopping boards. Butchers Broom has no leaves but modified flattened parts of stems called 'Cladodes" which in season hold flowers in their centres. The true leaves are much reduced in size to reduce water loss for the Butchers Broom can survive in very dry areas (it is commonly seen in Mediterranean scrub).    Late in March, Sweet Violet (Viola odorata) with its dark fragrant flowers starts to bloom near this cottage.

In the woods proper, the Early Dog Violet (Viola reichenbachiana) carpets the woodland floor in April; as its name suggests it flowers earlier than the Common Dog Violet (V. riviniana) , even when the former is in deep shade and the latter in full sun. This differing flowering period reduces competition between the two species for their insect pollinators. The Early Dog Violet can be recognized by its narrower darker spur; it was previously thought to be rare in Carmarthenshire but it is quite frequent on calcareous soils such as those on the Carboniferous Limestone.

The rich soil of the woods has resulted in a profusion of Primroses (Primula vulgaris) and Wood Anemones (Anemone nemorosa) the latter having carmine flowers at one site. Carex pendula, a large handsome sedge occurs and the walls of the 30 - 40 ft. high gorge has much Wall Pennywort (Umbilicus rupestris).

It is worth mentioning that due to the steepness and height of the gorge that many parts of this "hidden valley" are decidedly dangerous and one point with a large waterfall is impassable. I have called it a "hidden valley" for the O.S. map does not in any way betray its scale and depth.

The humidity results in a richness of the fungus-lichen flora, with the Red Cup Fungus (Peziza coccinea) common and the trunks of some trees are adorned with a type of Dog Lichen (Peltigera horizontalis).

Gradually the valley opens out to the village of Pont-newydd and the Lower Gwendraeth Valley, which is again very rich in all forms of wildlife (but that is another article!)

In terms of birds the cwm is not exceptional but it does contain typical woodland birds of the area - Nuthatches, Woodpeckers, Treecreepers, Sparrowhawks and Dippers; the insects have not been studied but due to the possibility of this site being primary, ancient woodland (it is far too steep for cultivation and shows little sign of coppicing) it may prove productive. Certainly it is worth¬while to note the occurrence of Pillbugs (Armadillidium vulgare) in the leaf litter; although Pillbugs are common on the mature dunes of Pembrey Burrows they are rare locally in woodland.

Finally, for the patient searcher, the shales contain some fossils - brachiopods ("lamp shells"), called Lingula due to their tongue-like shells. This genus is now confined to mainly Japanese coastal waters but as a fossil it was widespread. Some fossil plant fragments may be found and some sandstone beds show "ripple marks" indicating that they were laid down in a beach-like environment c. 300 million years ago.

Access is difficult; the cwm is presumably privately owned but it can be entered from the road at SN444074.

THE NAME “CWM CLYDACH” is frequent in those areas settled by people of Irish stock in the Dark Ages (during the latter years of or just after the Roman occupation) There is, for example, a Cwm Clydach in Powys (a Grade 1 SSSI!) and A.J. Thomas' an authority on Welsh place-names gives the meaning of Clydach as a "wild stream with a rocky bed" and this would still be an accurate description of Cwm Clydach today.

R.J. Thomas: "Enwau Afonydd & Nentydd Cymru" Gwasg Prifysgol Cymru 1938