334 MINNESOTA BOTANICAL STUDIES 



them and leading up to the development of the climax formations, 

 as well as the terminology used, are those proposed by Clements in 

 Plant Succession. The nomenclature of ferns and flowering plants 

 is essentially that of the seventh edition of Gray's Manual. 



Climax Formations 



Minnesota may be divided into- three great regions according to 

 the final or climax vegetation which dominates them, viz., pine for- 

 est, deciduous forest, and prairie. The distribution of the three cli- 

 max formations may be indicated by the accompanying map (fig- 

 ure 1). 



Classification of Successions 



It has been customary to classify successions according to the 

 initial cause, but it has been pointed out by Clements (1916) that 

 such a classification is unnatural and unsatisfactory, since the same 

 climax type may result from several dififerent initiating causes. Suc- 

 cessions are accordingly classified as follows : 

 I. Primary Succession 



1. Hydrarch 



2. Xerarch 



II. Secondary Succession 

 Whether a succession is to be primary or secondary is deter- 

 mined by the initial cause which, by the extent to which the habitat 

 is disturbed, afifects the kind and amount of water present. Primary 

 successions may be subdivided into hydrarch and xerarch succes- 

 sions, depending upon the character of the initial stage. Those be- 

 ginning in water are called h5^drarch, those beginning in dry condi- 

 tions, xerarch (Cooper 1912). 



course of succession 



The course of succession is indicated by the zonation peculiar to 

 a region. Accordingly, the key to the order of succession and to 

 the factors which have controlled it is to be found in the study of 

 zonation and the existing conditions of the dififerent zones, or their 

 corresponding associes. 



In tracing the development of the climax, the effect of the vari- 

 ous causes of succession in producing new habitats will first be 

 considered briefly. In turn, the efifect of the ecesic and stabilizing 

 causes in determining the nature of the development to the final 



