1921] Smiley: Flora of the Sierra Nevada of California 59 



boulders strewn over the rock-fields. Only rarely are good-sized 

 meadows seen in the higher mountains.* 



Though the precise location of timber-line in a given place may be 

 a matter of difficulty and involve a consideration of many factors, 

 some of them at present too obscure for satisfactory review, yet 

 ultimately the last vestige of arborescent growth has been passed 

 (compare plates 1 and 2) and the alpine region definitely entered 

 which finds its superior limit at snow-line, where such a line exists, 

 as in the Cascades. But in the Sierra the existence of snow-line is 

 only to be inferred from the presence of vestigial glaciers at certain 

 points in the Yosemite district and in the mountains to the southward. 

 There is no place in the Sierra today where snowfall exceeds melting. 

 There are therefore no "eternal snows" in the Sierra and no restric- 

 tion upon the area open to occupation by suitable plants because of 

 the existence of a niveal region. 



But this alpine region is by no means a continuous area ; rather it 

 is everywhere broken up and only found on isolated summits in the 

 Sierran region adjacent to and southward of Lake Tahoe. At the 

 present day there is no truly alpine habitat between Lassen Peak and 

 Mt..Rose. In the Tahoe region, the summits of Pyramid Peak, Dicks 

 Peak, Freels Peak, and possibly the summit of Mt. Tallac are of alpine 

 character. South of the Tahoe district, islets of arctic-alpine plants 

 become increasingly numerous and in the high mountains above the 

 Yosemite Valley the total area occupied or open to colonization by 

 arctic-alpines becomes considerable, and the same is true for the south- 

 ern Sierra. This fragmental character of the arctic-alpine terrane 

 unquestionably reacts upon the flora in preventing the spread of its 

 component species ; many of them must be dependent upon more or less 

 fortuitous agencies for their dispersal. Yet the alpine region of the 

 Sierra in its present state offers certain possibilities for plant invasion 

 by appropriate types perhaps superior to those of the majority of the 

 western high mountain ranges. The very recency of its glaciation has 

 removed much of the competition to which an immigrant plant is, 

 as a rule, subjected and to which it usually succumbs; the high 

 gradient of the alpine region generally promotes landslips whereby a 

 former plant population is removed and free ground exposed for 

 colonization. The sporadic distribution of manj^ of the distinctive 

 alpine plants lends some support to the view that they are in fact 



* J. N. LeConte writes of a. camping place in the alpine region south of 

 Yosemite : ' ' This was one of those rare spots in the Sierra above the timber-line 

 where the grass covers the hills and valleys, like the Coast Eange in spring. ' ' Bull. 

 Sierra Club, vol. 7, pp. 1-22. 1909. 



