*>_' FORKST DlSTK'im'TlON 







spruce favors tin- western slope. On the other hand I'/niis /><!- 

 . Liiri.r nrr'nli nftilis and Pseudotsuga taxifolia are far 

 heavily represented on tin- eastern sidt> than on the west- 

 ern, forming respectively '2. (>. and lo' ' per cent on tlie western 

 side, as a'jainM J~>. -4 and 12.V/C on the drier eastern slope. 



Another feature of the difference is in the vertii-al distri- 

 bution of thr species. On the western side the lower limit of 

 distribution is from 700 to 1000 feet below that of the eastern 

 and the upper limits from 500 to 2000 feet lower. It is noticeable 

 also that certain species like the grand fir and western hemlock 

 are confined to a much narrower vertical range on the eastern 

 than the western slopes, falling within a /one of 1000 to 1 .">()() 

 feet in the former and of about 3000 feet in the latter case. 

 These facts can only be interpreted in terms of the moisture 

 conditions and the lower limits of temperature encountered at 

 the higher altitudes. Several species listed in the table were 

 not of sufficient importance to merit calculation as to their 

 quantitative relations in the forest. 



The third or Clearwater section lies on the western slope of 

 the Bitter Root Range and embraces the drainage of the upper 

 branches of the Clearwater, its North, Middle and South Forks. 

 The area reaches the summit of the Bitter Uooi divide on the 

 east and (overs about 100 miles from north to south and from 

 4n to (in cast and west. The course of its principal streams is 

 mainly westward to a junction with the Snake Ifiver. 



In its northern part the forest vegetation is more nearly 

 re!,-iti-d to that of the western slope of the Coeur d'Alenes. The 

 white pinr. jn-bor \-it;ie Lirand fir and Douglas spruce are the 

 dominant species. In its southern part these species appear 

 very sparingly, and the dominant species an- yellow and lodue- 

 |">l- pim-x ;ind Ihiii'jhis spruce. I n this part the climatic con- 

 ditions an- inerjiii"- into these of the arid plains of the Snake 

 Valley. The marked variations in the pi-rcrnta.uv f different 

 Bpeciefl will thus be interpr-'ted accordingly. 



