THE PINON-CEDAR WOODLAND. 197 



southeastern in position, and is thought to represent the original mass of the 

 formation. The second is central and typical, while the last is Californian and 

 its relationship is less definite. The first two are in contact with each other for 

 a long distance, but they are readily distinguished by the presence or absence 

 of Juniperus pachyphloea and the evergreen oaks. The California association 

 is separated from the other two by the Colorado and Mohave Deserts and the 

 Sierra Nevada, and the dominants mix but slightly. Pinus monophylla and 

 Juniperus californica are the two species which maintain the contact between 

 the associations. This contact is in no wise as close or significant as that 

 between the two eastern associations, but this seems adequately explained 

 by the barriers mentioned. In other respects especially, the Pinus-Quercus 

 community appears much more nearly related to the woodland than to any 

 other climax. 



Contacts. — The woodland climax occupies the position indicated by its 

 vegetation-form, viz, the small evergreen tree. This is true both geographi- 

 cally and successionally, except where one or more dominants occur outside 

 of the climax area. At its lower limit it is regularly in contact with scrub of 

 some type, usually sagebrush or chaparral, rarely desert scrub. In the region 

 of the latter, the contact is usually with Prosopis savannah or with the Parkin- 

 sonia-Cereus scrub, or the oak mass itself shades out into a savannah domi- 

 nated by Bouteloua and Andropogon. Throughout its central area in the Great 

 Basin, sagebrush is everywhere in touch with the woodland, though some- 

 times mixed with chaparral. Along the eastern ranges of the Rocky Moun- 

 tains and in California, the contact is with chaparral. At the upper edge, 

 woodland is almost universally in touch with the montane forest, and par- 

 ticularly the Pinus ponderosa consociation, which is the most xeroid. The 

 contact may also be with a mixture of Pinus with Pseudotsuga mucronata or 

 Abies concolor, or with either of the latter consociations alone. This last case 

 is infrequent, however, and usually occurs where the yellow pine is absent or 

 unimportant. Successionally, woodland yields to yellow pine forest in the 

 ecotone between the two climaxes, especially during the wet phase of major 

 sun-spot cycles. Outside of the climax region, where it is represented by cedar 

 especially, it gives way to the chaparral, sagebrush, or grassland climax with 

 which it is in contact. 



THE PINON-CEDAR WOODLAND. 



PINUS-JUNIPERUS ASSOCIATION. 



Nature and extent. — This association is the most typical and definite of the 

 three that constitute the woodland climax. It usually consists of two domi- 

 nants, Pinus and Juniperus, which are regularly associated. They are similar 

 in character and requirements, and hence give a much more uniform physiog- 

 nomy than is found in the other two communities. This type of woodland 

 occurs most frequently in narrow belts a mile or less to a few miles wide along 

 the foothills of ranges from the Front Range of the Rocky Mountains to the 

 eastern slopes of the Sierra Nevada. On the north it ranges from the southern 

 edge of Idaho and Wyoming to Lower California, central Arizona, and New 

 Mexico. Its most typical expression is found in the center of this great region 

 on the high plateaus of the Colorado River. In such areas it forms more or 



