PLANT SUCCESSIONS OF MT. ROBSON 



229 



especially on hillock summits and on the outer slope, that are 

 entirely bare of plants and humus. 



It is at once evident that upon this moraine the two communi- 

 ties already described are still existent. The Dryas-Arcto- 

 staphylos Community, though well developed in certain spots, has 

 long passed its period of dominance. The Salix-Betula Commu- 

 nity is far better developed than upon the second moraine. But 

 it in turn is here in serious competition with a third community, 

 the Climax Forest, which is represented by Picea, Pinus, and 



Fig. 6. Vegetation upon Moraine I. Open forest of Picea Engelmanni and 

 thicket of Salix and Betula glandulosa. 



Abies, and by Pyrola and Moneses in the undergrowth. Sufficient 

 time has not elapsed since the deposition of the first moraine to 

 allow the forest to attain to its fullest perfection, but the trend 

 is plainly towards its establishment, with the consequent elimi- 

 nation of the two earlier stages. 



The Moraine Succession thus includes three stages: 1. Dryas- 

 Arctostaphylos; 2. Salix-Betula; 3. Climax Forest. All these 

 have their beginnings together upon the bare moraine, and all 

 are still existent upon the oldest deposit. They attain domi- 



