Area: 78.4 hectares.
Thorne Moor is common land.
Description and Reasons for Notification:
This site is one of the largest remaining areas of unimproved grassland and mire on the Culm Measures of North Devon. It has considerable botanical diversity and a rich associated fauna, including several nationally rare or scarce invertebrate species.
The moors are situated on Carboniferous shale deposits which are mostly overlain by acidic, clay rich soils. The land slopes gently on either side of a tributary of the River Torridge and the drainage conditions vary from restricted to waterlogged.
The vegetation comprises a range of grassland types with patches of scrub. Much of the grassland area contains abundant purple moor-grass Molinia caerulea, which is associated with a number of different plant communities. Over a large part of the site dwarf shrubs such as western gorse Ulex gallii, cross-leaved heath Erica tetralix, heather Calluna vulgaris and creeping willow Salix repens are abundant, while the local petty whin Genista anglica is also present. Sedge species such as carnation sedge Carex panicea, common sedge C. nigra, star sedge C. echinata, flea sedge C. pulicaris and tawny sedge C. hostiana are common. A wide range of grassland herbs characteristic of acid soils occur including whorled caraway Carum verticillatum, heath spotted-orchid Dactylorhiza maculata, meadow thistle Cirsium dissectum, sneezewort Achillea ptarmica, devil’s-bit scabious Succisa pratensis and lousewort Pedicularis sylvatica. Lesser butterfly-orchid Platanthera bifolia, lesser skullcap Scutellaria minor and bog pimpernel Anagallis tenella are restricted to small, well grazed areas.
Not all the grassland is acidic and on parts of the better drained ground species such as selfheal Prunella vulgaris, common knapweed Centaurea nigra, bird’s-foot-trefoil Lotus corniculatus and burnet-saxifrage Pimpinella saxifraga are indicative of neutral conditions.
The wettest areas are the richest botanically. Here there are elements of both acidic and neutral mire plant communities. The former are characterized by bog-mosses Sphagnum spp., sharp-flowered rush Juncus acutiflorus, many-stalked spike-rush Eleocharis multicaulis, common cottongrass Eriophorum angustifolium, bog asphodel Narthecium ossifragum, marsh lousewort Pedicularis palustris and marsh St John’s-wort Hypericum elodes. The latter have abundant soft-rush Juncus effusus and compact rush J. conglomeratus, with marsh-marigold Caltha palustris, common valerian Valeriana officinalis, wild angelica Angelica sylvestris, ragged-robin Lychnis flos-cuculi, meadowsweet Filipendula ulmaria, marsh cinquefoil Potentilla palustris and bogbean Menyanthes trifoliata. Also found in these areas are wavy St John’s-wort Hypericum undulatum, which is a nationally scarce plant, the locally uncommon bottle sedge Carex rostrata, and white sedge C. curta which is rare in Devon.
The scrub communities can be divided into those occurring in the waterlogged areas which are dominated by sallows Salix spp. and those on the drier ground where gorse Ulex europaeus, bramble Rubus fruticosus and bracken Pteridium aquilinum form the dominant species in association with herbs such as heath bedstraw Galium saxatile and slender St John’s-wort Hypericum pulchrum.
The site has a rich invertebrate fauna which includes three Red Data Book Species, the fairy shrimp Chirocephalus diaphanus* and two flies Microdon mutabilis and Sapromyza albiceps, and four nationally scarce species namely two flies Spania nigra and Chyliza vittata, the marsh fritillary butterfly Eurodryas aurinia and tiny beetle Atomaria rubida.
Common lizard Lacerta vivipara and adder Vipera berus both occur, while the breeding bird population is known to include grasshopper warbler Locustella naevia, reed bunting Emberiza schoeniclus, tree pipit Anthus trivialis, curlew Numenius arquata and stonechat Saxicola torquata.