 The site is nationally important for its south-western lowland heath communities and for transitions from ancient semi-natural woodland through upland heath to blanket mire.The site is also of importance for its breeding bird communities, its large population of the nationally rare heath fritillary butterfly ("Mellicta athalia"), an exceptional woodland lichen flora and its palynological interest of deep peat on the Chains.The ancient woodland is mostly to be found around Horner and Hawkcombe Woods near Porlock where it is open to the moorland and is grazed by domestic stock and red deer ("Cervus elaphus") of which there is a large population.