40 A Study of the Vegetation of 
Cedar Mt., 1914 
Pinus Larix- Thuja Pinus Larix- Thuja 
Conso- Abies Conso- Conso- Abies Conso- 
cies | Mictium ciation cies Mictium ciation 
Depth, 2 inches Depth, 10 inches 
(iliysgt: reer eco see oe 2F.02C@!|) SrAls 13.0 17.0 10.0 10.0 
uly’ 28... bes eels 3 coe 18.5 13.0 I2.0 16.0 II.0 10.5 
Jathy 25+ iat. ewes oles Geers 19.5 I2.0 TESOl | WPacveceie cote 10.5 9.5 
Auigtist iso eri: 18.0 FEB 6.57 21.0 T2355 II.5 
+ 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. 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 
