1907] 



YOUNG—FOREST FORMATIONS OF COLORADO 



345 



formation 



Where 



overlaps the pine formations on the ridges, its secondary layer is the 

 same as already described for them. In the canon bottoms it is 

 invading the Populus angustifolia-Salix ISTuttallii formation, while 



invaded bv forms from 



Where 



the tree growth is dense, however, it is practically exclusive of all 



Fig. 10. — The Picea-Abies formation; approximate altitute s^oo^; in the back- 

 ground is seen an extensive burned area. 



forms except a few mosses and lichens and an occasional Pyrola 

 secunda or Arnica cord i folia. The formation has been lumbered 

 extensively, the Douglas fir being used to a considerable extent for 

 rough bridge timbering and similar purposes. 



For the physical characters of the habitat, reference may be made 

 to the results recorded for the Pinus scopulorum formation, and for 

 Station A in the Pinus Murrayana formation, since both of these sets 

 of results are representative of the higher, drier parts of the Pseudot- 



