THE CONTINENTAL FLORA OF SOUTH SWEDEN 295 



Chapter IX. 



Distribution of Steppe Species and Sarmatian Psammophilous Species 



in South Sweden. 



As has already been pointed out, the scope of this work does not permit me 

 to enter into any detailed account of the distribution of species or any exhaus- 

 tive discussion of the numerous and interesting problems thus brought for- 

 ward. As to the distribution I have only to refer to the maps and the state- 

 ments given in Appendix I. In what follows I must confine myself to treating 

 the distribution from the points of view that seem to me to be, generally speaking, 

 most fundamental. Hence I shall examine how far certain ecological features, 

 which, to judge from the general distribution and mode of occurrence, may be 

 characteristic of the species, are reflected in the principal traits of the South 

 Swedish distribution: i. e. the heliophily of the species and their demands with 

 regard to the nature of the soil and climatic conditions. At the same time, 

 however, I shall try to prove the influence of two other important factors, viz. 

 the change in the natural vegetation of South Sweden by human interference and 

 the immigration history of the species. 



The possibilities of occurrence of the species in South Sweden if the 

 vegetation were unaffected by human interference. 



The great demand of steppe plants for light must be looked upon as a spe- 

 cially important ecological feature. Numerous examples show that the occurrence 

 of the steppe species may be primarily dependent on the supply of habitats 

 where this demand can be satisfied. 



In the Boreal forest zone, where, except in sporadic spots, a shady wood- 

 layer ought to cover the whole ground, this ecological character should in a high 

 degree determine the distribution of the species. But in extensive districts the 

 hand of man has removed or thinned the forests and thus created numerous lo- 

 calities for a heliophilous ground flora. It has thus in a high degree been able 

 to change the natural distribution of the heliophilous species. 



An endeavour to imagine the South Swedish vegetation brought back to its 

 natural state and to establish the possibilities of occurrence of steppe species in 

 such a vegetation — such an endeavour would be of great importance for the 

 explanation of the character of the South Swedish flora. In certain cases a 

 similar investigation may also be of great importance for the explanation of the 



