Area: 123.6 hectares.
The site is owned by the National Trust and lies within both the Dartmoor National Park and within the Devon Structure Plan’s Dartmoor Nature Conservation Zone. Hembury Castle is a Scheduled Ancient Monument.
The site includes good examples of semi-natural oak woodland and is representative of oak-woods developed on soils derived from the rocks of western and northern Britain. Also included are examples of valley alder wood and unimproved heathy grassland. It is an important entomological site.
Hembury Woods lies on the slopes and the intervening plateau of two valleys cut by the River Dart and its tributary the Holy Brook. Soils are derived from the shales, slates and grits of the upper Devonian and Carboniferous Culm Measures. The site has an altitudinal range of from 60–178 metres. The majority of the woodland is dominated by pedunculate oak Quercus robur, with silver birch Betula pendula also present. The understorey comprises mainly common gorse Ulex europaeus, holly Ilex aquifolium and locally, hazel Corylus avellana, with a vigorous development of woody climbers and ramblers, notably ivy Hedera helix, honeysuckle Lonicera periclymenum and bramble Rubus fruticosus. The ground vegetation is characterised by the abundance of bluebell Hyacinthoides non-scripta, great woodrush Luzula sylvatica, wood sage Teucrium scorodonia, bilberry Vaccinium myrtillus and common cow-wheat Melampyrum pratense and also by the presence of climbing corydalis Corydalis claviculata. Adjacent to the River Dart a strip of valley alderwood occurs and here oak again dominates but alder Alnus glutinosa is common and there is a rich ground flora which includes wood spurge Euphorbia amygdaloides, primrose Primula vulgaris, wood anemone Anemone nemorosa, ramsons Allium ursinum and an abundance of wild daffodil Narcissus pseudonarcissus. The royal fern Osmunda regalis occurs locally.
The trunks and branches of the trees and shrubs support a diverse lichen flora. A lichen of restricted occurrence, Phlyctis agelaea, occurs on beech Fagus sylvatica, with Pannari sampaiana, a lichen of very rare occurrence in England, also recorded.
Other habitats present include scrub, heath, bracken and herb-rich heathy pasture. The pasture is dominated by bristle bent Agrostis setacea and the sward is also characterised by the abundance of heath-grass Danthonia decumbens, carnation sedge Carex panicea, pill sedge C. pilulifera, autumn hawkbit Leontodon autumnalis, fairy flax Linum catharticum and tormentil Potentilla erecta and by the presence of carline thistle Carlina vulgaris and wild thyme Thymus polytrichus. Shrubs such as gorse and bell heather Erica cinerea, also occur.
The variety of habitats supports a rich invertebrate fauna and the site is an important entomological locality. Of additional interest are two mining adits adjacent to the River Dart which are used as winter roosts by small numbers of greater horseshoe and lesser horseshoe bats Rhinolophus ferrum-equinum and R . hipposideros.