 In addition to the Exmoor Coastal Heaths Site of Special Scientific Interest ( SSSI ) , two other areas are specifically designated . North Exmoor covers 12 @,@ 005 @.@ 3 hectares ( 29 @,@ 666 acres ) and includes the Dunkery Beacon and the Holnicote and Horner Water Nature Conservation Review sites , and the Chains Geological Conservation Review site . The Chains site is nationally important for its south @-@ western lowland heath communities and for transitions from Ancient 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 ( <unk> <unk> ) , an exceptional woodland lichen flora and its palynological interest of deep peat on the Chains . 
