PROBLEMS OF IMMIGRATION AND DISPERSAL 

 OF THE SCANDINAVIAN FLORA 



Knut F^gri 



Botanical Museum, University of Bergen, Bergen, Norway 



In discussing the characteristics of the Scandinavian ilora, botanists have, since 

 Blytt's days at least, been inclined to speak of and think in "flora elements". 



The concept of a flora element presumes a high degree of generahzation, 

 which is not always unambiguous. If Scandinavian phytogeographers speak 

 about the West-Arctic flora element, they think of a group of plants with a 

 certain total geographical distribution outside of Scandinavia. If they speak 

 of an oceanic element, distribution within Scandinavia is meant. A flora 

 element may even be defined by temporal relations, or by ecological ones. 

 Even if these ambiguities are under control the generalization as such is 

 dangerous. A common distribution area does not in itself explain anything. 

 On the contrary, it is a problem in itself, and what is generally done, is to 

 consider the hypothetical explanation of the reason why a group of plants 

 occur together as a fact to be used in the analysis of other problems as well. 

 But in nature there is nothing like a flora element behaving as a collective 

 unit. There are only individual plants (not plant species!) reacting each in an 

 individual way. And the more or less fortuitous occurring together may be 

 the result of widely differing histories and ecologic demands. 



Like that of any area, the flora of Scandinavia comprises elements of 

 different age. Leaving apart the endemic element — which is in our case 

 insignificant — we may summarize the history of any plant by the following 

 main points : 



1 . Origin and road of immigration. 



2. Dispersal during immigration. 



3. Conditions in Scandinavia at immigration. 



4. History of the plant in Scandinavia after immigration. 



In the current discussion these points have been taken into consideration in 

 varying degree, as they are also of diff"erent importance for different plants. 



The simplest group to explain is that of the most recent immigrants, the 

 anthropochorous apophytes. The importance of this group of plants increases 

 with increasing intensity of traffic, whereas increasing "cleanliness" and 

 efficiency of modern transport counteracts the spread of such plants. Ouren 

 has recently (1959) shown that a maximum of "transport efficiency" of 



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