Vegetation of Northern Cape Breton. 387 



character trees of the deciduous cHmax formation disappear in 

 approximately the following order : beech ; hemlock ; oak and 

 sugar maple; white pine; red maple; yellow birch. Except 

 for the two species last named, none of these are represented 

 in the evergreen coniferous climax forests of the highland. The 

 yellow birch, however, is frequently encountered here in edaphi- 

 cally favorable situations, while the red maple is commonly 

 represented bv shrubby specimens, which, however, seldom 

 attain the dignity of trees. It is also significant that for some 

 distance above the level where it ceases to occupy a prominent 

 position in the forest, the sugar maple still maintains an impor- 

 tant place in the undergrowth, being represented here by more 

 or less abundant, scraggly, shrubby specimens, which exhibit 

 unmistakable evidence of having been repeatedly killed back. It 

 is further significant that there is a marked correlation between 

 the vertical distribution of most of these trees in northern Cape 

 Breton and their north-and-south geographic range ; and it is 

 of interest to observe that toward its vipper limits the deciduovis- 

 mixed forest commonly is dominated by the yellow birch. 



The facts just presented, and particularly the complete 

 absence on the plateau, even in the many situations which are 

 edaphically favorable, of beech, sugar maple and oak, hemlock 

 and white pine, would seem to indicate conclusively that the 

 factors responsible for the character of the climax association- 

 type here are climatic and not edaphic. The controlling factor 

 in determining the upward extension of the deciduous forest 

 climatic formation is probably temperature (see discussion else- 

 where under head of climate). But atmospheric humidity may 

 also be a decisive factor, since the upper limit of the deciduous 

 climax forest coincides approximately with the lower limit of 

 the low-lying cloud belt in dull weather, a feature which has been 

 commented on earlier (p. 274). 



The status of the barrens, from the standpoint of ecological 

 plant geography. — The barrens are of peculiar interest, since 

 they present essentially the same type of vegetation that prevails 

 over vast areas on the Labrador Peninsula and throughout north- 

 ern Canada, regions concerning which almost nothing is known 

 ecologically. So distinct in its general aspect from that of the 

 forest region proper is the vegetation of the barrens that it was 

 at first thought to constitute a distinct climatic formation. 



