102 FOREST DISTRIBUTIOX 



seape in the Bitter Koot and the Jocko Valleys. Even low undu- 

 lations on the mountainside present the same aspect. Where 

 the direction of the slopes fails to present a sufficient contrast 

 of conditions the transition is more gradual and scattered forest 

 trees are sprinkled through the grass land diminishing in size 

 and numbers with the increase in distance from the main stand 

 until the farthest limits of the forest are represented by a few 

 low pines set at wide intervals. A tension between the prairie 

 and the forest is evident. It is also evident that the forest is 

 gradually replacing the grasses. Here the pine leads the way 

 followed closely by the Douglas spruce, these two and rarely 

 other species, Juniprrus scopulorum. The migration is usually 

 from above downward, but local conditions may var^- this and 

 show a migration from wooded canyons onto the neighboring 

 prairie. An interesting reversal of the usual course is to be 

 seen on Wild Horse Island in Flathead Lake, where the forest, 

 governed apparently by the proximity of the lake waters, became 

 established first at the foot of the slopes and is gradually oc- 

 cupying the higher groiind. 



Owing to local features of the physiography the directions 

 of the wooded and barren slopes may be altered, or even re- 

 versed. The western slopes of the ilission Range, rising from 

 Flathead Lake are densely wooded and steep, while the opposite 

 shore, a .series of low foothills, is mainly grass-land. The evi- 

 dent explanation here lies in the influence of the lake upon the 

 moisture content of the westerly winds. The foothills of the 

 west shore lie in the rain-shadow of the Cabinets, a high range 

 to the west. Narrow valleys or canyons extending north and 

 south and transverse to the direction of the west winds some- 

 times show the western slope more heavily wooded than the 

 eastern. This fact is due, apparently, to the protection from the 

 desiccating influence of the westerly winds afforded by the 

 mountain opposite and the normally higher temperature of a 

 western exposure. In the vicinity of TIaugan, near the western 

 boundary of the State, the dry exposures are distinctly north- 

 eastern. This locality was once heavily forested but many years 

 ago was denuded by fire. A s,a-ies of slopes here shows a sharp 

 contrast between the southwestern and western exposures which 

 were, at the time of the observation, in imO, producins; a sturdy 



