cent, was the chief dominant, growing in the uppermost layer, 

 while the other dominants, Bouteloua gracilis and B. curtipendula, 

 with about 10 per cent in cover and 100 per cent in constancy, 

 were in a lower layer. Most of the other species covered less than 

 about 3 per cent, although the frequency of some was high. 



Most of the analytical qualities, however, play a part in deter- 

 mining dominance. An excellent example is Andropogon gerardi 

 which, for many reasons, is the most important dominant in 

 broad lowland valleys in the tallgrass prairie region of the United 

 States (Figure 4-1). It forms the topmost layer of herbage, has a 

 deep and dense root system, tillers early, and has a long growing 

 season. It also possesses excellent vigor, sod life-form, and a high 

 degree of sociability; it forms almost complete foliage cover, has 

 good ground cover, has a frequency index of 100 per cent, and 

 produces a large yield in dry weight of from 400 to 725 g per sq m. 

 Another outstanding dominant, occurring in pastures, is orchard- 

 grass, which owes its success to excellent vitality, rapid growth of 

 roots and shoots which starts early in the spring, a widely 

 spreading and deeply penetrating root system, large crowns and 

 good herbage cover, high frequency, and dense bunches. The 

 annual, Bromus tectorum, apparently first noticed in the United 

 States around the year 1900, has become dominant on millions 

 of acres of the western range because of its large seed production, 

 rapid germination and growth of shoots and roots when condi- 

 tions are favorable, early maturity, and adjustment to drought 

 and other unfavorable conditions such as overgrazing. 



Physiognomy and Pattern 



Physiognomy, the appearance or "look" of a stand, may be 

 considered a synthetic quality because the appearance of vegeta- 

 tion is based on a number of qualitative and quantitative 

 characteristics such as the kinds and dominance of species, life- 

 form, population density, cover, height, sociability, stratification, 

 association of species, and color. For example, the sod-like blue 

 gramagrass-buffalograss type on the Great Plains differs strikingly 

 in physiognomy from the little bluestem-bunchgrass type — in life- 

 form, in the area of ground left bare, in height, in number of 



130 • TKe Comxnunity 



