Northern Plains Forest of Canada 33 



During the season of 1914, a considerable amount of time was 

 spent in the study of these types in the Pelican Mountain country 

 of northern Alberta. An area of some 3,000 square miles was 

 covered and the types were found to be distributed in the follow- 

 ing proportions : Boulder clay slopes type, 50 per cent, of land 

 area examined ; swamp muskeg type, 32 per cent. ; sand ridge 

 type, 18 per cent. 



The Boulder Clay Slopes Type — The soil of this type ranges 

 from clays to loams and varies greatly as regards the amount of 

 space occupied by the transported striated boulders. Three asso- 

 ciations occur within this type. 



1. The Pure Spruce Association, 1.3 per cent, of area of 

 the type, is found in small, widely scattered patches. The com- 

 position appears as follows : White spruce, 81 per cent. ; Balsam 

 poplar, 7 per cent. ; Aspen, 6 per cent ; White birch, 6 per cent. 

 Average density, 300 stems per acre. 



2. The Mixed Spruce Poplar Association, SO per cent, of 

 area of the type in which the spruce reaches its greatest indi- 

 vidual development in mixture with the poplar and birch. The 

 composition was found to be as below: 



Number per Acre Aver. D. B. H. Composition 



Inches Per Cent 



White spruce 110 12 31 



Aspen 132 10 38 



Balsam poplar 60 7 17 



White birch 53 5 14 



353 



The understory was composed of willow and alder and was 

 rather dense. This association appears to be unstable and in 

 process of transition towards the spruce association. 



3. The Pure Poplar Association, 53.3 per cent, of area of 

 the type, is the most widespread association of the Slopes type. 

 It exhibits a variety of conditions but is typically a mixture of 

 aspen and Balsam poplar with occasionally considerable amounts 

 of birch intermixed. While ordinarily regarded as a temporary 

 formation, it should be emphasized that in this northern forest the 

 poplars often form permanent stands, due perhaps to lack of ef- 

 fective competition but nevertheless maintaining themselves in- 

 definitely. The composition appears as follows : Aspen, QQ> per 

 cent. ; Balsam poplar, 23 per cent. ; birch, 8 per cent. Average 

 density, 140 stems per acre. 



