CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 



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The transition from subalpine forest to alpine tundra is usually 

 gradual with a thinning out of trees, which here commonly have 

 the dwarfed and distorted form known as Krummholz. Character- 

 istic of timber line are several trees that cannot survive in the 

 tundra above and cannot compete with climax species below, 

 where they are only found on dry and windswept ridges. Foxtail 



FlG. 133. Foxtail pine (Pinas aristata) Krummholz at timber line of the 

 subalpine zone in Colorado— U. S. Forest Service. 



pine (Pinus aristata) occupies this position in the southern Rockies, 

 limber pine (P. flexilis) in the central Rockies, whitebark pine (P. 

 albicaulis), and alpine larch (Larix lyallii) in the northern Rockies, 

 except in the far north where lodgepole pine occurs at timber line. 

 Douglas Fir Climax.— Below the subalpine zone, Douglas fir 

 (Pseudotsuga taxifolia) is the climax dominant, growing in such 

 dense stands that subordinate species are negligible. As in the sub- 

 alpine zone, climax associates differ in the north and south. In the 

 central and southern Rockies, white fir (Abies concolor) and blue 

 spruce (Picea pungens) are found in relatively small numbers and 

 mostly on moist sites. In the north, grand fir (Abies grandis) is an 

 associate west of the continental divide and principally on west 

 slopes. East of the divide, Picea glauca of the northern conifer 



