7$ A Study of the Vegetation of 



in all directions so that a single plant may cover an area 'of sev- 

 eral square meters. It is frequently so abundant as to form a 

 dense tangle very difficult to penetrate. Other common shrubs 

 associating with it are Ceanothus sanguineus, Pachistima myr- 

 sinitis, Salix scouleriana, Holodiscus discolor, and Spiraea corym- 

 bosa. On these steep, gravelly slopes the role of the shrubs in 

 catching surface washed materials including coniferous seeds 

 which are frequently buried under the debris, and in shading the 1 

 soil against excessive evaporation, is an important one in the 

 establishment of the tree stage in succession. Of the forest trees, 

 Pinids ponderosa and Pdeiidotsuga mucronata are most likely 

 to be found in such situations. 



The Pinus-Pseudotsuga Associes 



Although much of the forest in this region has been cut over 

 and still larger areas swept by forest fires, yet large tracts repre- 

 senting all the consocies and mictia of the region are still found 

 in their primeval condition. This is due to the rough topography 

 which makes them 'inaccessible to the lumberman, while certain 

 areas have been set aside by the federal government as mineral 

 lands. 



The above associes represents types of forest which occupy the 

 drier mountain slopes and are the transition stage from the grass 

 land and shrub to the more mesophytic forest communities. 

 Here are included the yellow pine and the Douglas fir consocies 

 and a pine-fir mictium. The former is the earliest in point of 

 succession and will be considered first. 



Pinus Consocies. Of all the forest trees of the region the 

 yellow pine is best fitted for the pioneer work of foresting prairie, 

 chaparral, or rocky areas. It overcomes xerophytic conditions in 

 part by striking its root-system deeply and spreading it widely, 

 thus laying hold upon large areas of soil. Rooted in rock crev- 

 ices it may make a height growth of only a fraction of an inch a 

 year and at the age of 40 or 50 years be only a few feet high, yet 

 such examples bear witness to its wonderful powers of resisting 

 adverse conditions. 



The difficulties of pines in invading grass lands should be recog- 



78 



