Vegetation of Northern Cape Breton. 275 



is the plant association: any group or community of plants, 

 taken in its entirety, which occupies a common habitat. Asso- 

 ciations which are correlated with a common type of habitat 

 and which are ecologically equivalent to one another may be 

 referred to a common association-type. The culminating mem- 

 ber of any specific successional series is termed an edaphic 

 climax association. In favorable situations this edaphic climax 

 coincides with the regional climax association-type: the most 

 mesophytic type of vegetation of which the climate of the 

 region permits the development on ordinary uplands. But, in 

 unfavorable situations, the edaphic climax may be represented 

 by an association which is less mesophytic than the regional 

 climax type. 



Parenthetically, it may be remarked that while emphasis is 

 usually placed, as above, on the relatively high degree of meso- 

 phytism which characterizes the regional climax association-type. 

 it is quite likely that this conception, while in general doubtless 

 holding true, should be altered somewhat. In the lowland of 

 northern Cape Breton, for example, a coniferous forest associa- 

 tion on ordinary uplands represents either a temporary stage, 

 destined to give way to deciduous forest, or else an edaphic 

 climax (see definition below) ; yet not infrequently, in so far 

 as their relative mesophytism is concerned, such forests seem 

 quite on a par with forests of the regional climax type. The 

 dififerentiating factors concerned in this particular case are sug- 

 gested in the writer's discussion of the ecological relations of the 

 balsam fir (p. 285). 



In any unit area where more than one association is repre- 

 sented, the associations, taken collectively, constitute an associa- 

 tion-complex. Within any specific geographic region the 

 associations are grouped naturally into a series of more or less 

 definite complexes with reference to the physiographic features 

 of the region, i. e., with reference to topography and soil. Any 

 association-complex which is thus related to a specific physio- 

 graphic unit area constitutes an edaphic formation. Edaphic 

 formations which are correlated with a common type of 

 physiographic unit area may be referred to a common edaphic 

 formation-type. The edaphic formations of any unit area, 

 where more than one is present, taken collectively, constitute 

 an edaphic formation-complex. The edaphic formation-complex. 



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