220 WILLIAM S. COOPER 



comes to be a mixed conifer-birch aggregation. The elimina- 

 tion of the hght-requiring birches and the complete dominance 

 of the climax conifers is now a mere matter of time. 



The development of the tree contingent may progress at 

 least as far as the mixed birch-conifer condition before any 

 considerable amount of lower growth appears. The establish- 

 ment of the smaller plants awaits and depends upon that of the 

 trees. Around, and largely below some of the willow bushes 

 growing upon open talus were found small patches of humus 

 and mosses, with occasional seedling conifers. Even in places 

 where the birches and conifers were rather closely placed, the 

 ground cover was little more extensive than this. Patches of 

 Arctostaphylos Uva-ursi (L.) Spreng., Dryas octopetala L., D. 

 Druminondii Richards, with occasional plants of Shepherdia 

 canadensis (L.) Nutt., representing a pioneer undergrowth stage, 

 alternated with areas of bare talus. A few individuals of Pyrola 

 uliginosa, P. secunda L., and forest mosses indicated the approach- 

 ing dominance of the true forest undergrowth. 



At the foot of this slope there is a large accumulation of talus 

 in the form of a ridge, parallel to the slope but separated from 

 it by a depression some scores of feet wide. The reason for the 

 separation is quite possibly to be found in the probable former 

 presence of a large snow bank, over the surface of which the 

 fallen blocks rolled. The disappearance of the snow bank with 

 change of climate has left the talus accumulation separated from 

 the main slope by a considerable depression. This explanation 

 has been applied with plausibility to similar cases elsewhere. 

 At any rate, the present accumulation is certainly talus, and it 

 bears climax forest fully developed. Because of its location in 

 the tension belt between the two zones, trees of both are present. 

 Picea Engelmanni is most abundant, and Abies lasiocarpa is 

 second. Pseudotsuga mucronata, Thuja plicata, Pinus Murrayana 

 Oreg. Com., and Betula papyrifera complete the list. Abies 

 and Thuja are most important in the young growth, and both 

 reproduce abundantly by layering. The shrubs are Ledum 

 groenlandicum Oeder, Menziesia ferruginea, Fatsia horrida, 

 Viburnum paucifiorum Pylaie, and Juniperus sibirica Burgsd. 



