198 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



continuous forests many miles in extent. The trees are 20 to 40 feet high 

 and stand sufficiently close to shade three-fourths or more of the ground. 

 This results in a sparse though characteristic ground cover. Such extensive 

 stretches of woodland are typical of the Grand Canyon plateau in northern 

 Arizona and southern Utah and of the Mesa Verde and Uncompahgre plateaus 

 in southwestern Colorado. It is on these that the climax association is to be 

 seen at its best and its extent and importance fully appreciated (plate 45) . 



The woodland dominants also occur throughout the range of the associa- 

 tion as a subclimax community in relatively new areas. They are the distinc- 

 tive feature of rocky slopes and of cliffs and escarpments at elevations of 5,000 

 to 8,000 feet over most of the climax area. Single dominants may extend far 

 beyond the latter as subclimax in sagebrush, chaparral, or grassland. This is 

 especially true of Juniperus, but it holds for Pinus also in some measure. 

 Such serai communities are mixed in varying degrees with the dominants of 

 the climax in which they occur and frequently lead to the assumption that the 

 woodland dominant is a member of the sagebrush or chaparral. All of the 

 evidence contradicts this assumption, however, and supports the view that 

 this is merely the normal response to developmental processes where two 

 climaxes occupy a broad and greatly interrupted ecotone. The contacts of 

 this association are essentially those already indicated for the formation, 

 namely, sagebrush and chaparral below and montane forest above. At its 

 own level, it touches the Quercus- Juniperus association broadly from Arizona 

 to Texas, and comes into fragmentary contact with the Pinus-Quercus com- 

 munity in CaUfomia. 



DOMINANTS. 



juntperus occtdentali8 monosperma. pintjs edulis. 



Juniperus californica utahensis. Pinus edulis monophtlla. 



Juniperus virginiana scopulorum. 



The most important of the dominants are Pinus edulis and Juniperus 

 monosperma. They occupy by far the major portion of the climax area, and 

 are regularly associated. Juniperus scopulorum has much the widest range, 

 especially northward, but it is usually of secondary importance in the com- 

 munity. The other four dominants exhibit two interesting and novel correla- 

 tions. Pinus monophylla and Juniperus utahensis are regular associates in the 

 western half of the climax, as are P. edulis and J. monosperma in the eastern. 

 Moreover, they are complementary forms, the latter dominating the associa- 

 tion through Colorado and most of New Mexico, Arizona, and Utah, the former 

 in Nevada and California. In western Utah and northwestern Arizona the 

 ranges of these four dominants overlap. 



In this common region, all five dominants may occur together, but this is 

 rare. The association of the four just mentioned is less so, but it is infrequent 

 at best. The general rule is that Pinus edulis and J. monosperma, or P. 

 monophylla and J. utahensis occur together, or that either one of the pifions 

 is found with both of the cedars. In Colorado and New Mexico at least, it is 

 not uncommon to find P. edulis associated with both J. monosperma and J. 

 scopulorum, though usually in the more open and less typical stands. With 

 the exception of J. scopulorum, all of the dominants frequently occur in pure 

 stands, but this is usually a consequence of differentiation by altitude. 



