Monday, 28 May 2012

Meirionnydd Naturalists: Trawscoed, 23rd February 2012 Andrew Graham

A narrow band of Ordovician ‘limestone’ can be traced for many miles across the Meirionnydd countryside, south from Llyn Celyn, (where it has been named the ‘Derfel Limestone’) down to the Bala fault and then, with a three kilometre sideways displacement, it can be picked up again and followed along the eastern side of the Arans. This narrow stratum was laid down in shallow water conditions which supported a shelly fauna whose physical remains still influence the plants (and animals) occurring here. The word limestone is rather an exaggeration and would not be used by a modern geologist but, to the botanist, the difference between this rock and the acidic rocks that dominate the surrounding areas is very apparent.

Four members of Meirionydd Naturalists Group (Rod Gritten, David Elias, Annie Seddon and myself) assembled at Trawscoed farmhouse and spent the morning examining the bryophytes and lichens growing along this ‘limestone’, mostly on and amongst ash trees. We were fortunate that the weather was dry and pleasant but the previous day had been exceptionally wet so both the bryophytes and the lichens were in fine condition. Indeed they looked so splendid it would have been hard for anyone not to be enthused.

All four British Lobaria species were found though, it was pointed out that some of these were present as the result of transplants carried out in the 1990s. Lobaria virens, in particular, was not known from the area previously and is a definite introduction. All the lichens seemed to be growing vigorously with the orbs of Lobaria amplissima evidently doing particularly well. Two Sticta species were found, with one ash tree supporting an impressive growth of Sticta fuliginosa. This lichen was on a horizontal branch quite high above the ground and would be easily missed by anyone simply staring at the trunks. Mosses characteristic of basic conditions were noted, especially by Annie, e.g. Ctenidium molluscum, Cirriphyllum piliferum and carpets of Rhytidiadelphus triquetrus.

Rod pointed out an interesting fungus, Hymenochaete corrugata, that ‘glues’ together hazel branches. This fungus has been recorded previously at this locality but the extraordinary gluing feature was new to the rest of us. One hypothesis is that the twigs that get stuck together stay above the ground and are thus out of the reach of competing fungi. For once the invented vernacular name Glue Fungus, is so appropriate and memorable that I, for one, will find it hard to avoid using it in future.

We walked on into the Trawscoed flower meadow, which was looking rather dull at this time of year, and a Plagiomnium species was collected and examined. This moss seems impossible to name confidently as it has a mixture of characters, some suggesting P. affine and others closer to P. elatum. Even after microscopic examination doubt remains as the cell size and shape is in the middle of the overlapping ranges given by the Moss Flora of Britain and Ireland, 2nd edition. The habitat and growth form probably favour it being P. affine but the long, broadly decurrent auricles are picked out in the books as a feature of P. elatum. The suspicion remains that bryophytes have been studied so intensively that species have been split to the point where specimens can no longer be assigned to one taxon or another except possibly by a handful of specialists.

After lunch, in comfort indoors, Rod had to leave but the rest of the party visited Coed Gordderw. This old estate woodland is not a natural wood – though it is becoming naturalised - and is dominated by the tree species favoured by a past generation of foresters, e.g. Beech, European Larch, Scots Pine and Norway Spruce. However, the trees are now so old that they have acquired an interest and the whole wood is unmanaged and very little visited so that it has the feel of an ancient woodland. Of particular interest is the abundance of Usnea filipendula in the higher parts of the wood, i.e. extending up to almost 500m a.s.l. This beard lichen is not especially rare but it is unusual to see such a luxuriant growth and, in fact, the comment was made that there was a resemblance to woodland in other less polluted parts of the world such as on African mountains.

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