CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 261 



to be restricted to moist and cool sites and extends into the next 

 lower zone only in such habitats. It, therefore, holds a postclimax 

 relationship to the climax below. Subalpine and alpine zones tend 

 to be drier and colder than the zones below, and, consequently, 

 preclimax and postclimax relationships may be reversed above the 

 montane zone. 



FlG. 131. Virgin Engelmann spruce (Picea engelmamii), with some alpine 

 fir (Abies lasiocarpa) of the subalpine zone in Colorado.— U. S. Forest Service. 



Subalpine Spruce-Fir Climax— From timber line downward for 

 about two thousand feet, the climax forest is made up largely of 

 Engelmann spruce (Picea engelwmnnii) and subalpine fir (Abies 

 lasiocarpa), which grow in dense stands. The spruce is the larger 

 and more abundant tree. In Arizona, New Mexico, and southward, 

 Abies lasiocarpa var. arizonica is as important as A. lasiocarpa. In 

 Montana and northern Idaho, mountain hemlock (Tsuga merten- 

 siana) is often found in the zone, and still farther north, approach- 

 ing the merging with northern conifer forest, Picea glauca and 

 A. lasiocarpa may grow in association. 



Subordinate species vary far more than do the dominants. On 

 the relatively dry eastern slope of the central Rockies, ground 



