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1000449

Status: Site of Special Scientific Interest (SSSI) notified under Section 28 of the Wildlifeand Countryside Act 1981 (as amended) Local Planning Authority: EXMOOR NATIONAL PARK AUTHORITY, SOMERSETCOUNTY COUNCIL, DEVON COUNTY COUNCIL National Grid Reference: SS 850349–915284 Other Information:The site includes the Somerset Trust for Nature Conservation's Mounsey Wood NatureReserve and Knaplock and North Barton SSSI notified in 1954. Site boundary amendedby extension. Site within Exmoor National Park. Part of the site was previously andseparately notified as Burridge Wood in 1983.
Description:The Barle Valley contains extensive tracts of ancient upland Sessile Oak woodland whichexhibit variations in structure and species composition as a result of difference in pastmanagement, geology and topography. There is a wide range of vascular plants includingmany ancient woodland indicators. The diversity of the site is increased substantially byareas of valley mire, heathland and acid grassland. The richness of lichens and bryophytesis of exceptional national importance and is significant internationally. There is also anoutstanding assemblage of breeding woodland birds and high invertebrate interestincluding nationally vulnerable and scarce species.
The site lies on Devonian sandstones, siltstones and slates from the Pickwell Down Bedsand Morte slates which have been deeply incised by the meandering course of the RiverBarle to form a valley of asymmetric profile. Steeply eroded slopes have thin soils withfrequent rock outcrops and boulder scree while flat alluvial terraces have formed throughdeposition of river sediment in the narrow valley bottom. Soils are from the Manod seriesbeing well drained, fine, loamy or silty. The soils over sandstones are thin, leached andpredominantly acid increasing in base status over shales, and in nutrients where flushedby river water. Woodland ranges in altitude between 150 and 300m on the valley slopes.
These grade into heathland and grassland on Whiterocks Downs and Ashway Side whichin turn rise to 360m. Annual precipitation reaches 1500mm.
The majority of woodland is dominated by Sessile Oak Quercus petraea. This ispredominantly of ancient origin and was formerly coppiced with some stands singled togrow on as high forest. Downy Birch Betula pubescens is abundant on the most acid soilsover steep sandstone slopes. The field layer comprises highly calcifuge species such asBilberry Vaccinium myrtillus and Wavy Hair-grass Deschampsia flexuosa. Holly Ilexaquifolium forms a sparse shrub layer in many stands of this type. The range of vascularplants is restricted but rich bryophyte communities thrive under these conditions. On thedeeper soils of the lower slopes Oak occurs with Hazel Corylus avellana and occasionalRowan Sorbus aucuparia. The field layer is more diverse including Creeping Soft-grassHolcus mollis, Common Bent Argostis capillaris, Wood Sorrel Oxalis acetosella,Bracken Pteridium aquilinum, Bluebell Hyacinthoides non-scripta and Dryopteris speciesas local dominants. Frequent members of this community include Enchanter's Nightshade Circaea lutetiana, Creeping Jenny Lysimachia nummularia and Common Cow-wheatMelampyrum pratense. Beech Fagus sylvatica has invaded this woodland type to varyingdegrees. Ash Fraxinus excelsior and Hazel become much more abundant over the base-rich shales. The well developed shrub layer here includes Hawthorn Crataegus monogynaand Blackthorn Prunus spinosa. The field layer is much more diverse. Eighty fivewoodland vascular plant species have been recorded including thirty one ancientwoodland indicators from a single compartment. Creeping Soft-grass, Dog's MercuryMercurialis perennis, Bluebell, Lesser Celandine Ranunculus ficaria and Common Dog-violet Viola riviniana are dominant members of the community. Species of note includeMoschatel Adoxa moschatellina, Wood Anenome Anenome nemorosa, PignutConopodium majus, Climbing Corydalis Corydalis claviculata, Early-purple OrchidOrchis mascula, Greater Butterfly-orchid Plantanthera chlorantha, Sanicle Saniculaeuropaea and Meadow saxifrage Saxifraga granulata which is rare and local in Somerset.
Dense groves of Hazel form ribbons along the alluvial terraces with a field layerdominated by Great Wood-rush Luzula sylvatica and Greater Stitchwort Stellariaholostea. Small stands of Alder Alnus glutinosa occur on water-logged flushes with aground flora of Tufted Hair-grass Deschampsia cespitosa, Greater Tussock-sedge Carexpaniculata, Bog-moss Sphagnum spp and the moss Rhizomnium punctatum.
Acid grasslands scattered along slopes and in coombes are dominated by Common Bentand Crested Dog's-tail Cynosurus cristatus. Frequent members of this community includeHeath Bedstraw Galium saxatile, Common Sorrel Rumex acetosa and Ribwort PlantainPlantago lanceolata. The meadows are one of the few sites for Great Burnet Sanguisorbaofficinalis on Exmoor. Springs emerging from the base of sandstone slopes generatenutrient poor acid mires dominated by Sphagnum and Polytrichum moss carpets,containing a community of Marsh Pennywort Hydrocotyle vulgaris, Marsh Violet Violapalustris, Meadow Thistle Cirsium dissectum and locally, Bog Asphodel Nartheciumossifragum and Lemon-scented Fern Oreopteris limbosperma. Ashway Side andWhiterocks Down support mosaics of acid grassland and heathland dominated by PurpleMoor-grass Molinia caerulea and Heather Calluna vulgaris on the plateau, while Brackendominates the slopes with Hawthorn and Gorse Ulex europaeus scrub scatteredthroughout. In wet areas Carnation Sedge Carex panicea and Lousewort Pedicularissylvatica are frequent associates while in drier parts Bell Heather Erica cinerea and HeathMilkwort Polygala serpyllifolia can be found.
The lichen flora is exceptional both for its luxuriance and in the number of rare species.
One hundred and sixty five taxa of epiphytic lichens are present containing a remarkablylarge proportion of ancient woodland indicators giving the Barle a very high index ofecological continuity. Ash and Hazel carry a Lobarion community which is particularlyrich on old boundary pollards and on trees growing on the river terraces. Species includeLobarion pulmonaria, L. laetevirens and L. scrobiculata the latter two being rare ancientwoodland species. Other examples, extremely rare in South West England includePseudocyphellaria crocata, Parmeliella jamessi, P. taylorensia and Nephroma parile.
Birch-Oak woodland carries a Parmelietum community characteristic of leached, wet,upland woods. Rare members include Heteroderma obscurata and Sphaerophorusglobosus. Alder stands host the rare oceanic lichen Menegazzia tenebrata while Hazelpossess smooth bark communities including the rare hyper-oceanic lichen Graphinaruiziana. In well lit situations in upper branches an Usneetum community is welldeveloped including Usnea articulata, a species largely confined to South West England.
Sandstone outcrops on north-facing slopes under Birch-Oak woods have an extremelyrich covering of oceanic bryophytes. Typical species include Bazzania trilobata,Scapania gracilis and Plagiochila spinulosa amongst which are species very rare inSomerset and the South West such as Lepidoza pinnata, Dicranum denudatum, Porellapinnata and Diphyscium foliosum. The ground layer is locally dominated by cushions ofDicranum majus, Plagiothecium undulatum and Rhytidiadelphus loreus.
The site contains an outstanding assemblage of woodland breeding birds includingparticularly high densities of Wood Warbler Phylloscopus sibilatrix, Redstart Phoenicurus phoenicurus and Pied Flycatcher Ficedula hypoleuca. The River Barleprovides an important habitat for Kingfisher Alcedo atthis, Dipper Cinclus cinclus andGrey Wagtail Motacilla cinerea, while scrub and heath have breeding Stonechat Saxicolatorquata and Whinchat Saxicola rubetra. Twenty species of butterfly have been recordedin the valley including the nationally scarce Marsh Fritillary Eurodryas aurinia andnationally vulnerable High Brown Fritillary Argynnis adippe. This species, in commonwith three other species of Fritillary in the valley use the plentiful supply of violet leavesunder Bracken as a larval food plant. The nationally scarce dipteran Sciapus longulus hasrecently been recorded here. Both Roe Deer Capreolus capreolus and Red Deer Cervuselaphus graze areas of wood pasture. The presence of Otters Lutra lutra on the Barle hasbeen regularly recorded. A colony of Dormice Muscardinus avellanarius inhabits at leastone of the Hazel coppices.

Source: http://somersetrivers.org/PDF/BarleValley.pdf