﻿SHAW— THE SELKIRKS 



489 



of course, according to altitude, topography, exposure, and moisture 

 content of the soil. 



Almost as important as altitude in determining the character 

 of the vegetation of a given area are topography and exposure to 

 light. While crags and ridges may be free from snow in May or 

 early June, the depressions between them frequently lie buried under 

 snow until the middle or latter part of July. These masses of wet 

 snow are apparently responsible for the drowning and suffocation of 

 the trees and larger srirubs in these depressions, as I suggested in 

 an earlier paper. 4 Other things being equal, the snow disappears 

 first from the east-facing and south-facing slopes; these slopes 

 therefore usually bear a more luxuriant and more varied vegetation 

 than those facing the west and north. It would seem that, in the 

 Selkirks, long-enduring snow masses, caused by heavy winter pre- 

 cipitations, topography, and exposure of the mountain slopes, are 

 the most important single factor in determining the distribution 

 of the alpine meadow and alpine desert vegetation. 



Among the trees which reach in scattered groups into the alpine 

 meadows, thus forming true "parklands," firs and spruces pre- 

 dominate. At 1800 m., in the lower portions of the belt, these retain 

 their characteristic conical form and frequently reach a height of 

 7 m. They are found most abundantly and are grouped most 

 effectively on slight elevations surrounding the numerous alpine 

 tarns of this newly glaciated country. At higher elevations, reach- 

 ing even to 2500 m., the firs and spruces exhibit the forms of wind 

 and snow cripples. Here they are associated with dense thickets of 

 juniper, and with occasional groups of the white-stemmed pine 

 {Pinus albicaulis). The thickets often cover the broader moun- 

 tain flanks, the gnarled cripples appearing in smaller groups or 

 singly on crags and narrow "sawbacks." An examination of the 

 rings of wood in the trunks of some of these cripples gave evidence, 

 as was to be expected, of extremely slow growth. Thus a fir, 40 cm. 

 in height and 2 . 5 cm. in diameter of trunk, cut near the summit of 

 Glacier Crest, between the Illicillewaet and Asulkan glaciers, 

 showed 62 wood rings. 



