78 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- 
sinmitis, Salix scouleriana, Holodiscus discolor, and Spiraea corym- 
bosa. On these steep, gravelly slopes the rdle of the shrubs in 
catching surface washed materials including coniferous seeds 
which are frequently buried under the debris, and in shading the 
soil against excessive evaporation, is an important one in the 
establishment of the tree stage in succession. Of the forest trees, 
Pinus ponderosa and Pseudotsuga 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- 
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