33^ 



General Botany 



U.S. Forest Service 

 Fig. 208. Pinon forest in northern Arizona, with sagebrush and grassland in the foreground, 



throughout the Western mountains, on flat areas are alpine 

 meadows, where the snow accumulates to great depths in the 

 winter. During July and August these meadows are covered 

 with the most briUiantly colored flowers. 



In general, alpine vegetation occurs at lower and lower levels 

 as we go north, but much depends upon the local exposure to 

 moisture-laden winds and whether the slopes face north or south. 

 North-facing slopes are moister and cooler and the growing season 

 is shorter than on slopes facing south. 



The forest trees of the Rocky Mountains are closely related 

 to those of the California-Puget Sound region. The upper limit 

 of tree growth is about 9000 feet in Montana and 12,000 feet in 

 southern Colorado. Since these mountains rise above an arid 

 plateau region, there is also a lower limit to tree growth ; this 

 limit is between 4000 and 6000 feet. In the Canadian Rockies 

 the forests are continuous in the broad valleys and mountain 

 slopes. Southward, beginning at Montana, the broad inter- 

 mountain valley is occupied by sagebrush semi-desert, and farther 

 south by desert vegetation. The most characteristic tree of the 

 entire region is the Western yellow pine. A close second is the 



