PLANT MIGRATIONS ACROSS THE NORTH 



ATLANTIC OCEAN AND THEIR IMPORTANCE 



FOR THE PALEOGEOGRAPHY OF THE REGION 



ElLIF Dahl 



Department of Botany, Agricultural College, Vollebekk, Norway 



It is a striking fact that the Arctic-Alpine floras on both sides of the North 

 Atlantic Ocean are very similar while this similarity does not extend to more 

 Temperate floras. A Scandinavian botanist feels quite at home in south 

 Greenland, whereas a French botanist working in areas of eastern America 

 with a cHmate corresponding to his homeland probably would recognize 

 most of the native genera but a few of the indigenous species. 



Many Arctic-Sub- Arctic species grow on both shores of the North Atlantic 

 Ocean, some being confined to that area while others have large gaps in their 

 distribution in Siberia or in western America. Such plants are said to have 

 an Amphi-Atlantic distribution pattern which has recently been beautifully 

 mapped by Hulten (1958). 



From Scandinavia to Scotland, the Faeroes, Iceland, east Greenland, 

 west Greenland, and into Canada, there seems to be a gradual transition 

 from a predominantly European flora in the east to a predominantly American 

 flora in the west. There are also very close phytogeographic connections 

 between Spitsbergen and northeast Greenland. This presents a problem since 

 it suggests that a direct migration has taken place. But the area is split apart by 

 long stretches of water and it is commonly supposed that migration of plants 

 and animals does not easily take place across large sea areas. This problem 

 has been discussed by numerous workers ; from earlier times might be mentioned 

 Hooker, Darwin, Warming, Nathorst, Blytt, and Ostenfeld and more recently 

 Fernald, Lynge, Nordhagen, Hulten, Nannfeldt, Bocher, and Love and Love. 

 Lindroth (1957) has recently treated the zoological and also some botanical 

 aspects of the problem in a very inspiring manner. 



TRANSPORT OF PLANTS BY MAN ACROSS THE ATLANTIC 



OCEAN 



Many plants and animals have been carried across oceans by human 

 traflic. Distribution patterns resulting from this transport should be excluded 

 from consideration in discussing the old phytogeographic connections between 



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