Einarr Rognvaldarson was nicknamed Torf-Einarr or Turf-Einar because he introduced the practice of burning turf or peat as fuel in the Orkney Islands, where there were no forests to provide wood for burning. This information is supported by various sources including Wikipedia, which states that "the sagas incorrectly claim that the Earl of Orkney was called 'Turf-Einarr' because he introduced the practice of burning turf or peat to the islands since there were no forests there" [1]. The Skaldic Project also mentions that his nickname 'Turf-Einarr' is due to his adoption of peat as a fuel in Orkney [2]. This nickname reflects his adaptation to the local conditions and resourcefulness in utilizing the available materials for heating and cooking.