Blackdown and Sampford Commons have the finest and most extensive surviving examples of the heathland, carr woodland and marshy grassland habitats that have developed on the acidic soils overlying the Greensand and Keuper Marls of the Blackdown Hills. The heathland supports a typical invertebrate fauna, including a wide variety of butterfly species, and with spiders notably abundant. The site is regionally important for birds which favour heathland habitats.