%M)^. 



Figure 1-8. While soil requirements of grassland, chief 

 species needle-and-thread {Stipa comata), must be secured 

 in deep soil with relatively few rocks, those of mountain 

 mahogany {Cercocarpus montanus) can be obtained in a 

 very rocky substratum. August, Front Range, Colorado. 



usually make less use of the environmental resources than those 

 in the later stages (Figure 1-7). 



Considerable variation exists between species in capacity to 

 utilize resources of the habitat (Figure 1-8). For example, Bromus 

 inermis and Agropyron smithii show greater response to nitrate 

 fertilizer than Bouteloua gracilis under similar conditions, and in 

 northern Colorado Stipa viridula and Agropyron smithii renew spring 

 growth earlier than Bouteloua gracilis, Buchloe dacty hides, and Aris- 

 tida longiseta. Vegetative growth of these species is usually com- 

 pleted by the latter part of June when the soil moisture has been 

 exhausted, but Buchloe and Bouteloua are able to renew growth 

 readily later in the summer if rains provide enough soil moisture; 

 Agropyron and Stipa, however, cannot grow well at the higher 

 temperatures. In western North Dakota the well -adapted species: 

 Agropyron smithii, Stipa comata, Bouteloua gracilis, Carex eleocharis, and 



Ecological Characteristics of Species & Populations 



23 



