Area: 172.4 hectares.
In Dartmoor National Park. In County Structure Plan Nature Conservation Zone. Boundary amended by extension and deletion.
Description and Reasons for Notification:
The site includes areas of ancient oak woodland of exceptional importance for the diversity of their lichen flora which contains many rare species. The oakwoods, together with the streams and marshes on the valley sides, are also important for their breeding populations of birds and invertebrates.
The site lies on the western edge of Dartmoor, primarily on the steep valley slopes of the River Walkham and its tributary streams. It ranges in altitude from 150 metres to 290 metres and is subject to a wet, mild Atlantic climate. On the slopes the soils are derived from the underlying coarse granite and are alluvial on the valley floor.
The woodland character is predominantly high forest and dominated by pedunculate oak Quercus robur which is in part derived from abandoned coppice. Ash Fraxinus excelsior, alder Alnus glutinosa and sycamore Acer pseudoplatanus occur on the valley floor. Beech Fagus sylvatica is found throughout. The understorey contains abundant hazel Corylus avellana, holly Ilex aquifolium, rowan Sorbus aucuparia and hawthorn Crataegus monogyna and, in wetter areas, sallow Salix cinerea and alder buckthorn Frangula alnus. On the drier slopes the ground flora is characterised by creeping soft-grass Holcus mollis, wood-sorrel Oxalis acetosella, bluebell Hyacinthoides non-scripta, pignut Conopodium majus and pramble Rubus fruticosus. Moss and fern communities are well developed in the more humid conditions beside the streams. Ferns include royal fern Osmunda regalis, scaly male-fern Dryopteris affinis, lemon-scented fern Thelypteris limbosperma and Tunbridge filmy-fern Hymenophyllum tunbrigense.
In response to the long history of woodland continuity and also to the pollution-free oceanic climate, a range of lichen communities has developed which reflects the variation in altitude and exposure to wind experienced within the site. In the sheltered valleys the Lobarioncommunity predominates, while higher up this grades into the Parmelietum laevigatae community which requires a higher rainfall. Among the many rare lichen species present are Heterodermia obscurata, Menegazzia terebrata, Lobaria scrobiculata, Pannaria mediterranea, Parmelia arnoldii, P. endochlora, Graphina pauciloculata, G. ruiziana and Cetrelia olivetorum.
Locally, water seeping down the hillsides gives rise to waterlogged conditions and the woodland gives way to open marshy areas often dominated by bog mosses Sphagnum spp. and purple moor-grass Molinia caerulea. Frequently occurring species include cross-leaved heath Erica tetralix, bog asphodel Narthecium ossifragum, common cotton-grass Eriophorum angustifolium, heath spotted orchid Dactylorhiza maculata, saw-wort Serratula tinctoria, devil’s-bit scabious Succisa pratensis and flea sedge Carex pulicaris. Small pools occur within the bogs, typical plants including hare’s-tail cotton-grass E. vaginatum, bog St John’s wort Hypericum elodes and bog pondweed Potomogeton polygonifolius.
The River Walkham and its tributaries are typical Dartmoor streams, being fast-flowing and nutrient-poor. The clean, well-oxygenated water supports an invertebrate fauna characteristic of torrent streams and the river is a major spawning ground for salmon Salmo salar and sea trout S. trutta trutta.
The site as a whole provides suitable habitat for a diverse bird community. Dipper Cinclus cinclus and grey wagtail Motacilla cinerea breed beside the river, whilst redstart Phoenicurus phoenicurus, buzzard Buteo buteo and wood warbler Phylloscopus sibilatrix breed in the woodland. The invertebrate fauna is also rich. Butterflies present include marsh fritillary Euphydryas aurinea, pearl-bordered fritillary Argynnis euphrosyne, silver-washed fritillary A. paphia, dark green Fritillary A. aglaia, green hairstreak Callophrys rubi and holly blue Celastrina argiolus.