Coedydd Dyffryn Alwen

Also within

Clwyd County

Habitats

Fast flowing river and stream

Geology & landscape

Geological Period: Ordovician · Rock Type: Alluvium, Glacial Till

Landscape processes: Fluvial, Glacial

Description

Description Coedydd Dyffryn Alwen extends 2.5 km along the steep sided valley of the Afon Alwen, 2 km downstream from Llanfihangel Glyn Myfyr, and approximately 8km north-west of Corwen. Elevation of the site ranges from 250 -280 m. The site is of special interest for its semi-natural broadleaved woodland, which for most of its length lines the riverbank. Geologically, the site consists of folded late Ordovician mudstones overlain in part by boulder clay and alluvium. The soil is very shallow in places, and rocky crags occur, particularly in the dingle south of Pencraig Fawr and along the river near Maes-cadw. Some base enrichment occurs where springs surface and along wet flushes, however the bulk of the woodland is on free draining acidic soils. The woodland vegetation is a complex mosaic of types, reflecting the above variations in topography and soil conditions. West of the Afon Alwen the site is dominated by ash Fraxinus excelsior and rowan Sorbus aucuparia woodland. The understorey is almost exclusively comprised of hazel Corylus avellana, with small amounts of goat willow Salix caprea and hawthorn Crataegus monogyna. The ground flora is more diverse, containing species such as dog’s mercury Mercurialis perennis, enchanter’s-nightshade Circaea lutetiana, and a range of ferns. In the most northwestern section, the ash woodland grades into alder Alnus glutinosa woodland on the wetter, flushed areas. Characteristic species here include opposite-leaved golden -saxifrage Chrysosplenium oppositifolium, common nettle Urtica dioica and patches of meadowseet Filipendula ulmaria. East of the Afon Alwen, sessile oak Quercus petraea and downy birch Betula pubescens woodland predominates. The ground flora is typically grassy, with sweet vernal -grass Anthoxanthum odoratum, common bent Agrostis capillaris and creeping soft-grass Holcus mollis along with wood-sorrel Oxalis acetosella and varying amounts of bluebell Hyacinthoides non-scripta. Where the soil is especially base-poor, heather Calluna vulgaris, great wood-rush Luzula sylvatica, bellheather Erica cinerea, wavy hair-grass Deschampsia flexuosa can be found. The locally scarce globeflower Trollius europaeus is recorded adjacent to the river, while colonies of oak fern Gymnocarpium dryopteris and beech fern Phegopteris connectilis can be found within the dingles. Non-native sycamore Acer pseudoplatanus can be found at very low density across most of the southern part of the site. Other non-natives include beech Fagus sylvatica and conifer species, but these are found only in a few small areas. The well-wooded and sheltered watercourses afford lying-up sites for otter Lutra lutra.

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