Glacial survival, post-glacial immigration, and a millenium of human impact: On search for a biogeography of Iceland.

Northern Europe was capped by ice during Weichsel (Wurm), the maximum of which occurred approximately 18,000 years before present. When in the latter part of the 19(th) century the view of an all-devastating land ice (the tabula rasa hypothesis) was generally adopted by natural scientists, plant biogeographers used a simple model predicting a post-glacial, northwards re-migration of species in continental Europe. Occurrence and distribution of species were the prestige words when the flora and fauna elements of all area were described, and active and passive dispersal by wind, waves and migrating animals were considered. At the turn of the century observations of the distributions of certain plant species in the Scandinavian high mountains did not tally with the accepted tabula rasa and migration hypotheses. As the importance of long-distance dispersal was questioned as a general model to explain the occurrence of species, an alternative hypothesis was proposed that predicted the occurrence of sites (refuges) permitting glacial Survival of species (the refugium hypothesis). As Iceland has been covered by ice - the extent of which is under debate still - and its position in the middle of the Atlantic the occurrence of many species was difficult to explain without resting on the novel hypothesis. The controversy between the Scandinavian advocates of the two alternative hypotheses over time is reflected in the interpretations of field studies focussing oil the occurrence and distribution of the Icelandic biota. Man arrived in Iceland recently, i.e. at the end of the 9(th) century. His appearance and colonization implied that another means of dispersal and establishment of biota had to be considered: man was and,is a conveyor of species to and within the island. Moreover, lie settled, cultivated land, and he and his livestock, often freely grazing, transformed the landscape and affected abundance and distribution of species. To optimize the yield of his farm the farmer made and makes decisions oil a micro-level with bearing upon flora and fauna. But decisions that ultimately affect biota were and are also made on a macro-level e.g. by the Icelandic and foreign Governments (actions against soil erosion, trade barriers, price policy). The context in which decisions are made have to be regarded when we discuss the biogeography of Iceland. Rarely, it is possible to separate the impact of man from that of other agents and to evaluate his effects on the occurrence and distribution of species in most areas. Maybe Iceland is such an area where it would be possible, as man has affected the ecosystems during a rather short period and his doings can be followed in written sources. Such a study requires all integrated scientific approach and is not a matter of a single biologist but a team of skilled scholars and natural scientists