Vegetation of Northern Cape Breton. 291 



of great importance during the northward migration of the 

 deciduous cHmax trees which has ensued in post-glacial time 

 (see especially Adams '02), and there is little question that in 

 parts of the transition region farther south, where balsam is 

 absent or restricted in its distribution, such factors are still of 

 large significance. 



General features of transition climax forests in northern Cape 

 Breton and elsezvhere. — The trees which characterize forests of 

 the climax type in the lowland of northern Cape Breton may be 

 divided into four groups, as follows: (A) Deciduous species, 

 such as the beech and sugar maple, whose center of distribution 

 lies south of the transition region; (B) Deciduous species, 

 notably the yellow birch, whose center of distribution lies within 

 the transition region; (C) Evergreen species, notably the hem- 

 lock, whose center of distribution lies within the transition 

 region; and (D) Evergreen species, such as the balsam fir and 

 white spruce, whose center of distribution lies north of the 

 transition region. To these might perhaps be added a fifth group: 

 (E) Deciduous species, such as the paper birch and the balsam 

 poplar, whose center of distribution lies north of the transition 

 region. 



It has been intimated in earlier paragraphs that the relative 

 abundance of the different climax trees is subject to considera- 

 ble local variation. By way of summary, it may be stated that 

 in forests of the regional climax type the trees of group A com- 

 monly predominate, though sometimes they are outnumbered by 

 those of group C. The yellow birch, representing group B, is 

 practically always present, varying greatly in abundance, usually 

 common though seldom predominant (but see in this connection 

 p. 387). The trees of group D are seldom completely absent: 

 usually they occupy a prominent, but rarely a predominant, posi- 

 tion in the forest. The trees of group E are commonly repre- 

 sented, but always as a minor element in the forest : frequently 

 they are missing altogether. 



While the above observations are made primarily with refer- 

 ence to conditions in northern Cape Breton, they are capable of 

 much wider application. Throughout much of the vast expanse 

 in eastern North America which is embraced by the transition 

 region, the five groups of trees specified in the preceding para- 

 graph are represented. Broadly speaking, throughout this area 



