86 



FOREST DISTRIBUTION 



The sixth section includes the Bitter Eoot Valley, an area 

 of about 3000 square miles. It is bounded on the west by the 

 summit of the Bitter Root ilountains and on the southeast it 

 reaches to the crest of the Continental Divide. On the east its 

 margin rests upon the top of the divide between the Bitter Eoot 

 River and Rock Creek. 



Finns ponderosa — 



contorta 



■' albicaidis - 



monticola 



Larix occldentalis 



Lijallii 



Picea Engelmannii 



Pseudotsuga taxi folia . 



Abies lasiocarpa 



" grandis 



Thuja plicata — - 



Juniperns scopulorum 



32.0 

 40.0 



9 



1.6 

 24.2 



3500-7000 

 3.500-SOOO 

 7500-8500 



3500-5000 

 7500-9000 

 3500-7500 

 3500-7000 

 5000-8000 

 4000-5000 

 4000-5000 



It win be observed that the prevailing species in this sec- 

 tion are those adapted to drier conditions, viz., the yeUow and 

 lodgepole pines and the Douglas spruce. All others are in a 

 small minority. The species of the humid forests, the white 

 pine and its associates, are now mostly confined to the upper 

 canj'ons of the Bitter Root R-ange. This conforms exactly to the 

 climatic conditions of the section. The Bitter Root Valley has 

 an annual precipitation record of 10.71 inches, representing the 

 average of a good many years of observation. This is a lower 

 figure than is shown at most of the plains stations in eastern 

 Montana. They are, however, the observations at only one sta- 

 tion that of Hamilton near the center of the valley. It is easy 

 to understand this condition since the whole valley is sheltered 

 on the west by the lofty Bitter Roots, which effectually intercept 

 the rain bearing western winds. The temperature of the Bitter 

 Root Valley is, moreover, usually a little higher than that of the 

 neighboring localities, which must further influence its water 

 supply. 



The lower limits of vertical distribution are < onsiderablv 



