264 THE STUDY OF PLANT COMMUNITIES ■ Chapter X 



FlG. 134. Montane zone climax forest of Douglas fir (Pseudotsuga taxi- 

 folia) and white fir (Abies concolor) in Colorado.— U. S. Forest Service. 



forest shares dominance with Douglas fir and extends southward 

 through the montane zone as far as the Black Hills. 



Dry, exposed ridges in both the montane and subalpine zones 

 support open stands of pine, including several species characteris- 

 tic of timber line. P'mus strobiformis is important in the south. P. 

 aristata occurs in northern Arizona and southern Utah and Colo- 



