CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 267 



favored by the grasses of the forest floor, they are rarely severe 

 enough to kill the fire-resistant older trees. That pine seedlings are 

 destroyed is indicated by the even-aged groups of saplings, each 

 of which can be related to a series of summers that were free of 

 fire. Severe fires in the upper part of the ponderosa pine zone may 

 be followed by stands of lodgepole pine. Lumbering and over- 

 grazing often result in the development of a dense scrub made up 

 of species from the oak-mountain mahogany zone. 



FlG. 137. Characteristic open stand of piiion- juniper, and the transition 

 from sagebrush desert —U. S. Forest Service. 



Vinon-Juniper Climax- This open forest of widely spaced, small 

 trees (ten to thirty feet) forms the lowest coniferous zone in the 

 Rockies and, on many of the low ranges of the Great Basin, repre- 

 sents the only zone present. It is, therefore, typical of the inter- 

 mountain region as well as forming a distinct zone in the southern 

 Rockies. Although it is fairly constant in appearance and charac- 

 teristics over its wide range and extensive acreage, several species 

 with restricted ranges are involved. The junipers include Juniperus 

 scopulorwn, J. monospermy J. utahensis, J. occidentalism J. pachy- 

 phloea, J. mexicana, and others, and the pinons, or nut pines, are 

 varieties of Finns cembroides (edulis, monophylla, parry ana). 



The type extends from northern Mexico along the west slope 

 of the Rockies to the Snake River in Idaho, beyond which it con- 

 tinues into southern Alberta with piiion replaced by limber pine. 

 Along the east slope, its northern limit is in Colorado although it 

 is represented northward through Wyoming by Juniperus scop- 



