Y Glyn-diffwys

Also within

Clwyd County

Habitats

Bracken scrub

Geology & landscape

Geological Feature: Gorge / Ravine · Geological Period: Ordovician

Landscape processes: Fluvial

Description

Description This site is notified as an example of a semi-natural ancient broadleaved woodland situated in the steeply incised section of the Afon Ceirw. Such wooded sections are rare in the former county of Clwyd. The woodland which occurs on acidic Ordovician rocks, has a canopy dominated by native tree species. Sessile oak Quercus petraea together with wych elm Ulmus glabra and less commonly ash Fraxinus excelsior are the principal species. The well-developed shrub layer is characterised by hazel Corylus avellana. The field layer is variable, reflecting the different steepness, aspect and soil conditions in the gorge. On the north side of the gorge, dog's mercury Mercurialis perennis, bluebell Hyacinthoides non-scripta, bramble Rubus fruticosus and ramsons Allium ursinum occur whilst to the south, ferns including several Dryopteris species are widespread together with bracken Pteridium aquilinum. Ericaceous shrubs are locally present. The gorge itself is singularly the most important feature supporting a number of uncommon higher plant and fern species including national rarities together with several species of Atlantic bryophytes. Atlantic bryophyte assemblages tend to be uncommon in Clwyd woodlands because of the lower rainfall and hence humidity. Important bryophyte species include the liverworts Porella pinnata and Plagiochila spinulosa together with the mosses Isothecium holtii and Hypnum callichroum.

Species mentioned

Insects to look out for

These moths, butterflies and beetles are known to feed on plants recorded at this site, and carry a notable UK conservation status — but a host-plant being present doesn't mean the insect has actually been recorded here. Treat this as "worth watching for," not a confirmed sighting.

Host-plant data: Cook et al. (2025), Traits data for the butterflies and macro-moths of Great Britain and Ireland, 2024, UK Centre for Ecology & Hydrology / Butterfly Conservation; and Padovani et al. (2020), Database of Insects and their Food Plants (DBIF), UK Centre for Ecology & Hydrology (both Open Government Licence). Contains data supplied by UK Centre for Ecology & Hydrology.

Plant communities