Complex sentence: The Blackdown Hills have, since 1991, been designated as an Area of Outstanding Natural Beauty (AONB) under the National Parks and Access to the Countryside Act 1949.
Split into simpler sentences: The Blackdown Hills have, since 1991, been designated as an Area of Outstanding Natural Beauty (AONB). AONBs are created under the same legislation as the national parks: the National Parks and Access to the Countryside Act 1949.