A Study of the Vegetation of 



Cedar Mt., 



t Readings taken at a depth of 2 feet. 



A discussion of light values as affecting succession had best be 

 given in connection with the study of the development of the 

 forest communities. 



THE PRAIRIE-PLAINS FORMATION 



The prairies represent an extreme westward extension of the 

 prairie-plains formation east of the Rocky Mountains. 1 This 

 great grass land area is here represented by the Agropyron- 

 Festuca association. It occupies a belt of varying width between 

 the desert scrub formation on the west and the Pacific Coast forest 

 formation on the east. Thus three vegetational frontiers are seen 

 to meet within the region covered by the present investigation. 

 Altitudinally, it occupies an area whose westward boundary has 

 an elevation of 1,200-1,300 feet, while eastward it reaches an 

 altitude of about 3,500 feet. 



The prairies are limited on the east by that combination of 

 climatic and edaphic factors which make tree growth possible, a 

 type of vegetation with which the prairie can not favorably com- 

 pete. The changed climatic conditions are largely due to in- 

 creased altitude and are especially expressed in greater precipita- 

 tion. Likewise, coniferous tree growth is demarked more or less 



1 At the present time, I am not quite clear whether we should properly 

 speak of the prairie-plains formation or whether, indeed, we have here two 

 grass land formations. In any case, the vegetation of the Agropyron- 

 Festuca association more nearly simulates that of the prairies proper, 

 Agropyron spicatum being an ecological equivalent of Andropogon sco- 

 parius east of the mountains. 



40 



