Vegetation of Northern Cape Breton. 399 



2. The Formation-types of Ordinary Uplands in the Barrens 



a. THE ASSOCIATION-COMPLEXES OF WELL-DRAINED UPLANDS 



The rock face-crevice complex. — Over most of the plateau the 

 bed rock is covered by a thin soil which may be residual or 

 extraneous in its origin. Here and there, however, rounded 

 knolls or blocks of granite and syenite rise conspicuously, and 

 on these may be found rock- face and crevice associations essen- 

 tially similar to those which have been described as characteristic 

 of rock outcrops in the lowland. 



But the prevailing pioneer type of vegetation on uplands in the 

 barrens is some sort of a heath. In the heath the lichens, notably 

 the cladonias, are invariably conspicuous, while sedges and 

 grasses, shrubs and scrubby trees occupy a position of varying 

 importance. 



The dwarf shrub heath association-type. — This is characteris- 

 tically developed on exposed hill tops, where the soil may sup- 

 port only the scantiest kind of a plant cover (foreground of Fig. 

 51). In such situations the ground in places is bare; elsewhere 

 it is overlain by a sparse mat of cladonias and Racomitrium 

 lannginosnm, or maintains a stubby growth of Polytrichmn 

 jnniperiniim, P. piliferum, and Ceratodon purpureus. Of the 

 seed plants peculiar to such habitats, Potentilla tridentata is 

 worthy of note, but particularly characteristic are the four 

 shrubs : Empetrum nigrum, which forms low, sprawling mats ; 

 Vaccinium uliginosum, which occurs in depressed circular 

 patches ; Vaccinium Vitis-Idaea, which scrambles over the 

 ground and frequently is intricately interwoven in the lichen mat ; 

 and Vaccinium pennsylvamciim angustifolium, a form of blue- 

 berry only a few inches high. In addition to these, there is 

 usually a scattering of other plants, particularly ericaceous 

 shrubs, all of which are noticeably impoverished. 



Typical dwarf shrub heath occurs locally throughout the bar- 

 rens, but in a pure state is nowhere extensively developed. In 

 exposed situations it may constitute a permanent association- 

 type, i. e., an edaphic climax. But more commonly it seems to 

 represent a temporary stage, destined to be superseded by dwarf 

 shrub-spruce heath, into which it nearly everywhere merges. 

 In places dwarf shrub heath very evidently is a retrogressive type 

 which has arisen subsequent to the destruction of dwarf shrub- 



