Theories on migration and history of the North-Atlantic flora: a review

Abstract

Two theories on migration and the history of the North Atlantic flora have been the subject of a popular debate for over a century. In late 19th century when signs of glaciations had been recognized in Scandinavia, it was concluded that the entire flora and fauna had been destroyed during glacial periods and that all plants immigrated after the last glacial period. This so called tabula rasa theory was soon opposed by the glacial survival theory which stated that plants survived the last or several of the Pleistocene glaciations in ice-free refugia within North Europe. The glacial survival theory was very popular, in the mid-20th century, notably because of three botanical arguments that were forwarded in its support: 1) it alone could explain the distribution of the so-called west arctic element e.g. species found in Scandinavia, Iceland and North America but missing in the Alps, Ural Mountains and Asia, 2) the alpine endemic element e.g. the relatively higher proportion of endemic species in the alpine flora of Scandinavia compared to the lowland, and 3) the special disjunction of the alpine flora. Later, those arguments were reconsidered for the Scandinavian flora and it was concluded that they could be explained without glacial survival. In the last decade, new techniques e.g. molecular methods, results from ice core projects and pollen analyses have offered fascinating possibilities to re-formulate the questions asked by research pioneers. The debate on the plant migration and origin of the flora in the North Atlantic region thus continues.