<P> Humans have lived in Shetland since the Mesolithic period . The earliest written references to the islands date to Roman times . The early historic period was dominated by Scandinavian influences, especially from Norway, and the islands did not become part of Scotland until the 15th century . When Scotland became part of the Kingdom of Great Britain in 1707, trade with northern Europe decreased . Fishing has continued to be an important aspect of the economy up to the present day . The discovery of North Sea oil in the 1970s significantly boosted Shetland's economy, employment and public sector revenues . </P> <P> The local way of life reflects the Scottish and Norse heritage of the isles, including the Up Helly Aa fire festival, and a strong musical tradition, especially the traditional fiddle style . The islands have produced a variety of writers of prose and poetry, often in the distinct Shetland dialect of Scots . There are numerous areas set aside to protect the local fauna and flora, including a number of important sea bird nesting sites . The Shetland pony and Shetland Sheepdog are two well - known Shetland animal breeds . Other local breeds include the Shetland sheep, cow, goose, and duck . The Shetland pig, or grice, has been extinct since about 1930 . </P> <P> The islands' motto, which appears on the Council's coat of arms, is "Með lögum skal land byggja ." This Old Norse phrase is taken from the Danish 1241 Basic Law, Code of Jutland, and is also mentioned in Njáls saga, and means "By law shall land be built". </P> <P> The name of Shetland is derived from the Old Norse words, hjalt (' hilt'), and land (' land'). </P>

Why are there no trees on shetland islands