Vegetation of Northern Cape Breton. 413 



for the forested region. It may occupy like situations in the 

 barrens, but here it also is a frequent type on moist, fairly well 

 drained hillsides which are protected from the wind. 



Summary of successional relations. — It will be seen that in a 

 general way the association-types of well-drained uplands in the 

 barrens have been arranged in an ascending series; that there 

 are all gradations between dwarf shrub heath and sedge-grass 

 heath at the one extreme and typical forest at the other. Incident 

 to the special discussion of the association-types, various succes- 

 sional relationships have been pointed out. But while it is con- 

 ceivable that in the course of time the associations of relatively 

 primitive types are everywhere destined to become superseded by 

 associations of more advanced types, as a matter of fact this is 

 not generally the case. For the degree of mesophytism capable 

 of attainment in the majority of sites is limited by edaphic 

 factors, and any of the association-types described above may 

 constitute locally an edaphic climax. 



b. THE ASSOCIATION-COMPLEXES OF POORLY DRAINED UPLANDS 



Although a distinction may be made between well-drained and 

 poorly drained uplands in the barrens, as a matter of fact, as has 

 been intimated earlier, it is practically impossible to draw sharp 

 lines of demarcation. Owing to the character of the vegetation, 

 especially to the influence of the almost universally developed 

 lichen-bryophyte ground cover in retarding drainage, an area 

 which originally may have been well-drained rapidly becomes less 

 so, and there are few areas in which water cannot be squeezed 

 out of a peaty substratum at almost any time of the year. 



In protected situations, wet, poorly drained uplands may sup- 

 port low, swampy forests of (mainly) black spruce, with an 

 undergrowth of Alnus incana, Osmunda cinnamomea, and the 

 like: forests w^hich might almost equally well be treated under 

 the head of hydrarch successions. Further, the occurrence of 

 sphagnum hummocks in areas occupied by heath has already 

 been mentioned. On flat upland areas from which the water 

 runs off slowly or where it tends to collect locally in shallow 

 rock basins, as well as in various other situations where drainage 

 conditions are such as to favor, at least locally, the development 

 of the sphagnums, bogs and boggy swamps may arise on uplands. 



