North Exmoor is a Site of Special Scientific Interest (SSSI) for its lowland heath and its transitions from ancient semi-natural (coppiced) woodland through upland heath to blanket mire (bog). It is especially noted for its breeding bird communities, exceptional woodland lichens and its large populations of nationally rare Heath and High Brown Fritillary butterflies (especially around the Horner area, thanks to the efforts of National Trust conservationists).
Most of the site's ancient woodland is around Horner, too, and is grazed by large herds of red deer. Sessile oak, silver birch and rowan cover the steep sides of the combes, with an understorey of bilberry (known as 'whortleberry' in Somerset). Woodland birds include pied flycatchers, wood warblers and redstarts, as well as redpolls and nightjars, while dippers and grey wagtails can be seen around the rivers and streams. Many of the moor's breeding birds are species usually found further north, such as merlins, ring ouzels and red grouse. Upland birds include buzzards, ravens, curlews and snipes, and whinchats and stonechats.
Over the centuries the pounding of the waves during winter storms finally breached the shingle barrier at Porlock Marshes, giving rise to an unusual coastal environment which is of international importance.
The Quantocks, too, are a SSSI, being one of the most extensive areas of semi-natural habitat in South West England. The range of habitats includes dry dwarf-shrub heath, wet dwarf-shrub heath, acidic flushes, ancient semi-natural woodland and dense scrub. Important local plant species are supported in the SSSI, and it has an outstanding bird population.
Heathland is important here, too, and is dominated by bracken, heather, gorse and bilberry, while important mosses and bog plants grow in the wetter areas. The woodland - again mostly sessile oak, with birch and rowan, with holly and hawthorn as well - has been extensively coppiced over the centuries to provide wood for tanners such as Thomas Poole and charcoal burners like John Walford. Valley woodland species include alder, ash, hazel, field maple and wych elm, and this area too is noted for its lichens.