8o A Study of the Vegetation of 



Creek, at a distance of 12 miles from any contiguous body of 

 timber. However, this is a phase of the problem which I found 

 little time to study. 



The yellow pine consoci-es forms the transition zone from 

 prairie or shrub to other types of woodland. In the mountains 

 it occupies exposed south or southwest slopes or only the tops of 

 these if the lower slopes are sheltered. Not infrequently it is 

 accompanied by Douglas fir. 



On the exposed buttes only scattered trees may occur among 

 the shrubs on north slopes. In other cases well developed for- 

 ests may be found. On higher buttes, the rocky tops, ravines, 

 and sheltered bases may be clothed with a pine forest, while large 

 stumps, or isolated pines towering above the Douglas fir and tam- 

 arack now in possession of the moist, sheltered slopes, tell the 

 story of a former occupation by a pine forest. Thus all stages 

 of development are strikingly shown on these butte ramparts of 

 the forest frontiers. Often on wind-swept ridges a sheltering 

 spur permits the growth of pines, while a slight descent from a 

 pine-clad ridge may reveal an entire change in tree dominants, 

 the Douglas fir and tamarack replacing the pine. 



As already indicated, the pines have worked their way down 

 the Palouse River and along Rock Lake. In the shallow canyons 

 they are practically confined to the sheltered canyon sides. Doug- 

 las fir and Larix accompany them in the deeper canyons of the 

 Palouse River, but I have found only the former with the pine 

 about Rock Lake. Opulaster pauciflorus invariably accompanies 

 these forest outposts and its distribution is undoubtedly due to 

 chipmunks and squirrels, which are likewise ever present in pine 

 woods. Numerous plants, which otherwise are found only in the 

 mountains also occur in these pine-clad canyons. Among others 

 Aconitum columbianum, Actaea spicata arguta, Thermo psis mon- 

 tana, and Veratrum viride may be mentioned. In fact, the study 

 of plant populations upon wooded buttes isolated by a distance 

 of from only a few to several miles from the forests proper is 

 fascinating and instructive, but one into which we can not well 

 enter here. 



The xerophytic conditions under which the pines grow about 



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