THE 'S^'ESTEKN VALLEYS 127 



of fine timber are in places so seriously affected as to make it 

 difficult to find a sound tree. 



The importance of this disease appears not only in the de- 

 preciation of the wood for commercial purposes but also in the 

 shortening- of the life of the tree and the lessening of its repro- 

 ductive vigor. The tree is also subject to serious attacks by 

 the bark beetle, Deudroctonus monticolae, and owing to the thin- 

 ness of its bark is readily injured by ground fires. 



All of these factors are then very potent influences in keep- 

 ing the tree within narrow geographic bounds and ordinarily 

 below a medium point numerically over areas which are capable 

 of supporting it. In Montana it is confined to the west side of 

 the Continental Divide. It doubtless reaches its most 

 southern limit in the Kocky ^Mountains in the Bitter Root range 

 between Montana and Idaho, possibly as far south as Nez Perce 

 Pass, at the head of the West Fori?: of the Bitter Root, and mostly 

 on the western or Clearwater slopes. 



The grand fir (Abies grandis) is nowhere in Montana a com- 

 mon tree. Even in the mesophytic forest to which it properly 

 belongs it is seldom conspicuous and it grows in poor form and 

 only to medium size, as compared with the sometimes pure stands 

 of fine, large trees to-be found here and there west of the Cas- 

 cades. The salient qualities of this tree may be set forth as fol- 

 lows: As to its positive characteristics, the grand fir grows 

 rapidly while young and has a considerable capacity to resist 

 shade. It appears not to be particular as to soil composition or 

 structure. The seeds are light and amply winged. On the 

 other hand it is not given to early fruitage in the Rocky Moun- 

 tains, and its seeds have transient vitality and low germi- 

 native capacity. It is not at any time prolific in the bearing of 

 seeds. The species is exacting in its moisture requirements and 

 its temperature range is rather narrow. In addition to these 

 traits the tree is susceptible to disease and is easily injured by 

 fire. 



Like the white pine the grand fir wins in competition mainly 

 by reason of its tolerance and rate of increase in height. The 

 early production of seed is a mark of some advantage in the 

 most favored parts of its range, but in the less favorable region 

 of the Rocky Mountains even this feature disappears. The seeds 



