SEWBReC Gwent Biodiversity Blitz Day 2007, Cwm-du


The first Gwent Biodiversity Blitz Day took place on 28th July 2007 at Cwm-du (Blaenserchan). It was arranged at quite short notice, and as a result was not well attended – in fact only four were present: Steve Williams, Peter Sturgess, David and Katherine Slade.

Cwm DuCwm-du is a narrow, steep valley running east – west for just over 2 km. Several coal-mines existed on the site, and the last of these was abandoned about fifteen years ago. The spoil from the mines was tipped around the valley sides and this now forms the dominant substrate. An access road runs along the northern side of the valley, heading down to the level of the former Blaenserchan Colliery. Above this road is an area of broadleaved woodland (the dominant trees being sessile oak and beech) and extensive areas of bracken. At the bottom of the valley runs the Nant Ddu, a small tributary of the Afon Llwyd.

Gall on Germander Speedwell (Veronica chamaedrys)A small clearing to the right of the provided some interest. Highlights in the uppers section of the site included a single Marbled White butterfly and small patches of Quaking Grass (Briza media) and galls on Gemander Speedwell (Veronica chamaedrys), caused by the fly Jaapiella veronicae.

The main spoil heaps were rich with lichen and fungi, including several black mushrooms (later identified as Entoloma chalybaeum var luzulinum). This is predominantly classed as calcareous grassland, and supports Grayling (Hipparchia semele), lots of Small cudweed (Filago minima) and Blue fleabane (Erigeron acer). Also, the large patches of bare earth and rocks favoured Mottled Grasshopper (Myrmelerotettix maculates) and several of these were seen.

On the track down to the stream had three Moonwort (Botrychium lunaria) and a single plant of Pearly Everlasting (Anaphalis margaritacea). Several Dark-green Fritillaries were very active along the course of the valley, pausing briefly to take nectar from Marsh Thistle (Cirsium palustre) and Hemp Agrimony (Eupatorium cannabinum).

Striking pink earth tongueIt is particularly unfortunate however that probably the best two records remain unconfirmed. The only Odonata to be seen was a damselfly that could only have been a male White-legged Damselfly (Platycnemis pennipes). It was caught by the stream, but escaped before it could be photographed or examined more critically. The other was a striking pink earth-tongue, which was spotted on the walk back  to the car beside on of the recently fenced off Adits. In hindsight, it does seem likely that it was the rare fungus Clavaria rosea, but it was not collected so cannot be confirmed.  

In all, 290 species were recorded, of which 192 were vascular plants. Download the full list of species recorded.