[From the Bulletin op the Torrey Botanical Club 40 : 677-686^ 6 J 1914.] 



Phytogeographical notes on the Rocky Mountain region 



I. Alpine region 



P. A. Rydberg 



The alpine region, roughly speaking, is the region between the 

 perpetual snow and the timber line. 



The upper limit, the perpetual snow line 



A perpetual snow line cannot be spoken of in the southern 

 Rockies. Even the highest peaks do not have a perpetual snow 

 cap like Mt. Shasta or Mt. Hood. This is probably due to the 

 less amount of moisture and precipitation. It is true that many 

 of the peaks have perpetual snow on them, but this snow is mostly 

 in the form of snow-drifts and small glaciers, especially on the 

 northern or northeastern side. The amount of snow depends to a 

 great extent on local conditions, as for instance on an exposure 

 to the northwestern winds or partial protection from the direct 

 action of the summer sun. The Snowy Range of Colorado has 

 more snow than the much higher Gray's Peak, Sierra Blanca, or 

 Mount Massive. In the Canadian Rockies and especially in the 

 Selkirk Mountains the conditions are different and more like those 

 of the European Alps. There the highest peaks have a perpetual 

 snowcap and the glaciers extend far down in the valleys. In 

 northern Montana, as for instance in the Sperry Glacier region, are 

 found the only places in the United States where in the Rockies 

 there are glaciers of any great extent, notwithstanding the fact 

 that the Montana mountains are considerably lower than those of 

 Colorado. 



The lower limit, the timber line 



The timber line is by no means a well-defined boundary line. 

 It is in reality a broad zone in which the woody vegetation gradually 

 thins out from the dense forest to the last krumholz. In 

 nature there is not found any sharp line between two regions, but 

 only a gradual transition zone between them. 



677 



LIBRARY 

 (NEW YORK 

 BOTANICAL 



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