Because of Dartmoor's height and granite geology, it experiences strong winds and has acidic soils. In consequence it has been subject to very little intensive farming, and all these factors combine to form the basis of the important ecosystems found here. The landscape is one of granite with peat bogs overlying it. While the moors topped with granite tors are the most iconic part of Dartmoor's landscape, only about half of Dartmoor is actually moorland. Equally important for wildlife are the blanket bogs, upland heaths and the oak woodlands which are all of global importance. Dartmoor is a Special Area of Conservation (SAC) with four habitats ("Northern Atlantic wet heaths with Erica tetralix"; "European dry heaths"; "Blanket bog"s and "Old sessile oak woods with Ilex and Blechnum in the British Isles") being listed as primary reasons for the selection of Dartmoor as a SAC. In addition the area has a population of the Southern damselfly which is also a primary reason for its selection along with populations of Atlantic salmon and Otter being qualifying reasons.