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Area: 323.73 hectares. 

The site is described in ‘A Nature Conservation Review’, edited by D. A. Ratcliffe, 1977, published by Cambridge University Press.
The site lies in the Dartmoor National Park, the Dartmoor Environmentally Sensitive Area, is within the Devon Structure Plan’s Dartmoor Nature Conservation Zone and adjoins the Bovey Valley SSSI. 

Description: 

The site comprises one of the best remaining ancient oak woodlands in Devon. Trendlebere Down – to the north of Yarner Wood – contains a mosaic of heathland, grassland and valley mire vegetation. 

Yarner Wood lies on the steep slopes of two valleys cut by small streams and on the intervening plateau. The soils are generally acid, peaty podzols, notable for their massive and very compact structure and are derived from underlying modified shales and mudstones of the Carboniferous Culm Measure series. In the south and west the podzols are replaced by more fertile brown earths. The site has a wide altitudinal range, varying from 79 metres and 311 metres and is subject to a wet, mild Atlantic climate. 

The woodland character is primarily high forest, dominated by sessile oak Quercus petraea and derived from abandoned oak coppice. On the acid podzols silver birch Betula pendula is common and the understorey contains abundant holly Ilex aquifolium and rowan Sorbus aucuparia. Honeysuckle Lonicera periclymenum and ivy Hedera helix occur abundantly, while the ground vegetation is characterised by the dominance of bilberry Vaccinium myrtillus and by the wide occurrence of common cow-wheat Melampyrum pratense, hard fern Blechnum spicant, broad buckler-fern Dryopteris dilatata and by a well-developed bryophyte mat. On the richer soils hazel Corylus avellana becomes significant in the understorey, while bramble Rubus fruticosus and creeping soft-grass Holcus mollis replace bilberry in the ground flora. The nests of the wood ant Formica rufa are a ubiquitous feature of the woodland floor. 

In the valley bottoms the woodland is dominated by downy birch Betula pubescens and alder Alnus glutinosa. In the wettest areas, alder carr predominates and the ground flora is characterised by bog-mosses Sphagnum spp., royal fern Osmunda regalis and greater tussock-sedge Carex paniculata. In the east lies a small valley bog dominated by purple moor-grass Molinia caerulea, heather Calluna vulgaris and bog myrtle Myrica gale

Heathland on Trendlebere Down to the north of Yarner Wood is dominated by heather and also contains abundant bell heather Erica cinerea, cross-leaved heath Erica tetralix, western gorse Ulex gallii, purple moor-grass and scrub birch. Secondary birch has also developed with bracken Pteridium aquilinum on the sites of old field systems, where there is active regeneration of oak. Sections of the heath within Yarner Wood National Nature Reserve have been subject to a long programme of controlled burning. Trendlebere Down contains valley mire vegetation with round-leaved sundew Drosera rotundifolia, bog asphodel Narthecium ossifragum, common cottongrass Eriophorum angustifolium and southern marsh-orchid Dactylorhiza praetermissa

The site supports a rich bryophyte flora and over 100 species of lichens have been recorded, including the tree lungwort Lobaria pulmonaria. The fern community is diverse with 15 species recorded including hay-scented buckler-fern Dryopteris aemula and Tunbridge filmy-fern Hymenophyllum tunbridgense.

The butterfly and moth fauna is rich, with over 650 species recorded. Characteristic butterflies include white admiral Limenitis camilla and high brown fritillary Argynnis adippe, while among the many moths present orange upperwing Jodia croceago and Devon carpet Lampropteryx otregiata are notable. 

The breeding bird community contains a wide variety of species typical of western oakwoods, including large populations of wood warbler Phylloscopus sibilatrix, pied flycatcher Ficedula hypoleuca and redstart Phoenicurus phoenicurus. On the heathland, there are breeding Dartford warblers Sylvia undata and nightjars Caprimulgus europaeus. Wintering hen harriers Circus cyaneus are occasionally seen. The breeding mammal fauna includes dormouse Muscardinus avellarinus.