256 



Origin of Biomes and Succession 



Pinon pine - 



juniper biome 



A . 



Rocky Mountoin 

 yellow pine biome 



A 



Alpine fir 

 Abies losiocorpa 



Spruce sp. 

 Piceo sp. 



Douglas fir 

 Pseudotsugo toxifolia 



White fir 

 Abies concolor 



Rocky Mt yellow pine 

 Pinus brochyptero 



Piiion pine 

 Pinus edulis 



Utah juniper 

 Juniperus utohensis 



Spruce -fir 

 biome 



A 



9 9.2 



100% or sum of 

 oil shaded areas 

 at any elevation 



Fig. 113. Histograms showing the relative abundance of the dominant tree 

 species in the Kaibab National Forest, Arizona. Numbers refer to elevation in 

 thousands of feet. (Adapted from Rasmussen.) 



bush-bur sage (Larrea-Franseria) biome grows on the finer soil 

 which has washed to the foot of the lower slopes and valleys. 

 Yang and Lowe point out that water content and availability are 

 remarkably different in the two types of soil and that these dif- 

 ferences are probably the basic reasons for the differences in veg- 

 etation. 



In the subdivisions within the biome (the associations of Shel- 

 ford) the abundant dominants are different species, but in each 

 subdivision the set of dominants superimposes essentially the same 

 modifications on the general environment. The biome may there- 

 fore contain several communities differing in specific rather than 

 general properties. 



Distinctive terrestrial biomes and their constituent communities 

 are therefore chance units based on the competitive superiority of 

 certain types of plants and the effect which the resulting dominant 

 plant species have in modifying the general ecological conditions 

 within the area of their dominance. 



As is evident from the analyses of Moore (1958) and Hedgpeth 

 (1957), the bottom marine communities may be and have been 

 classified along much the same lines as terrestrial communities. 



