13] 



VEGETATIONAL TYPES OF POLAR LANDS 



393 



the dominants themselves are much mixed, and usually they are 

 consolidated below by a layer of cryptogams in which Mosses or 

 Lichens commonly subdominate according to whether the situation 

 is relatively moist or dry, respectively. Fig. 117 shows an area of 

 dense mixed heath on the south shore of Hudson Strait. In the 

 drier situations there may occur frequent gaps in the heath which 

 are actually dominated by Lichens — particularly by ' Caribou-moss ' 

 Cladonias that may form a sward 5 or more cm. high. In depres- 

 sions and behind obstructions where snow drifts deeply in winter, 



Fig. 117. — Dense luu -arctic heath dominated b> Arctic Blueberry {I'accmium 



uligitiosuin var. alpmuni) in northernmost Quebec. Light-coloured Lichens and 



leaves of dwarf Willows and Sedges are visible. To the left of the sheath-knife 



is a lowering bushlet of I^apland Rose-bay (Rhododendron lapponicum). 



a characteristic dark (except when flowering) heath dominated by 

 Arctic Bell-heather usually develops, often with associated Sedges 

 and Mosses at least where the soil is lastingly moist. Such an area 

 is shown in Fig. 118 and, apart from a zone of more mixed heath 

 that may develop outside, usually constitutes the outermost of the 

 zoned series of subclimaxes developed in late-snoM^ areas as described 

 on pages 402-5. 



In the middle-arctic belt, heathlands are usually somewhat lower 

 in stature and more restricted in area than to the south, having the 

 appearance of postclimaxes developed in the most favourable situa- 

 tions. Of the cited dominants Mountain Cranberry has usuallv 



