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Phytogeographical notes on the Rocky Mountain region 

 IV. Forests of tiie Siibalpine and Montane Zones* 



p. A. Rydberg 



The mountain regions may be divided into four zones: (i) the 

 Alpine Zone, above the timberline; (2) the Subalpine Zone; (3) 

 the Montane Zone; (4) the Foothill Zone. These correspond 

 to Dr. Merriam's Arctic, Hudsonian, Canadian, and Transi- 

 tion life-zones, respectively. The Alpine Zone has already been 

 discussed by me in three preceding papers. The Subalpine and 

 Montane Zones are more or less mesophytic, while the Foothills 

 are decidedly xerophytic. The characteristic trees of the last 

 are the bull pines and nut-pines and the cedars, which there 

 seldom form dense woods, but grow more or less scattered on the 

 hillsides. The Subalpine and Montane Zones are characterized 

 (with the exception of the exposed ridges and larger open valleys 

 or "parks") by more or less dense woods of spruce, fir, pines and 

 aspen. Many do not distinguish these two zones, and no definite 

 line can be drawn between them. Most of the plants are common 

 to both; the most characteristic tree of the Subalpine Zone, the 

 Engelmann spruce, extends far down into the Montane Zone, and 

 several of the principal components of the latter, especially the 

 Douglas spruce, extend far up into the former. In general the 

 division line may be placed at the upper limit of growth of the 

 bull-pine and the lower of the subalpine fir. This varies con- 

 siderably. In Colorado it may be placed at an altitude of 3,000 m. 

 (10,000 ft.), in the Yellowstone National Park at 2,300-2,500 m. 

 (7,500-8,000 ft.), in the Glazier Park Region of Montana at 



* This article is not intended to present any new facts, but merely a summary. 

 The only feature as far as I know that has never been presented in print in this 

 form is the division line drawn between the Northern and Southern Rockies and the 

 reasons for drawing it at that particular place. The distribution of the forest 

 trees both altitudinally and geographically has been treated more extensively and 

 in greater detail elsewhere, both in the various "tree books" and in the reports from 

 the United States Forest Reserves, but a short resume is always desirable. 



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