CARRYING CAPACITY. 285 



lowing paragraphs, while their part in overgrazing is discussed in the next 

 section, and their relation to increased carrying capacity under that dealing 

 with range improvement. 



Relation to communities and dominants. The general value of climax 

 and serai communities as grazing indicators has already been discussed. This 

 is related directly to the carrying capacity, which is determined by the nature 

 of the dominants and subdominants and their groupings. The value of a 

 dominant is determined primarily by its total yield, palatability, and nutri- 

 tion content, but it is affected in the most striking fashion by associated 

 dominants. In fact, palatability is regularly the controlling factor, since a 

 grass of high yield and nutrition content may remain untouched in a com- 

 munity of more palatable species, while it may be completely utilized when 

 foi-ming a pure community or in the absence of more succulent forage. Thus, 

 the question of relative palatabiht> becomes of the first importance in the 

 study of overgrazing and of range improvement. It varies with the kind and 

 breed of stock, with the phases of the climatic cycle, and with the year or 

 season. 



With respect to total yield, the relative importance of dominants may 

 be best illustrated by the grassland climax. The tall-grasses produce more 

 forage than the short-grasses, and the sod-grasses more than the bunch- 

 grasses; but a tall bunch-grass, such as Agropyrum spicatum or Andropogon 

 hallii, may yield more heavily than a short-grass like BovieUma gracilis, though 

 the latter is more palatable and hence more completely utilized. A short- 

 grass like Bulbilis, which forms a compact turf, has a higher carrying capacity 

 than Bouteloua gracilis with an open turf, v/hile the latter excels the more 

 open B. eriopoda as well as the bunch-Uke B. rothrockii. A mixed community 

 of tall- and short-grasses has much the higjiest carrying capacity of all, and of 

 these the most productive is one in which the lower layer is Bulbilis. Sub- 

 dominants which approach the grasses in palatability have a similar r6le in 

 increasing carrying capacity, but the great majority are less palatable and 

 decreiise the yield in proportion to their luxuriance. Grasses also affect the 

 carrying capacity by virtue of different times of development. A community 

 which contains Stipa spartea or comata permits earlier grazing than others, 

 while a mixed prairie with Stipa, Agropyrum, and short-grasses not only 

 affords the longest season, but likewise the most continuous production of 

 forage. The relative yield of tall- and short-grasses is also affected by the rain- 

 fall of wet and dry periods. The yield of tall-grasses seems to be reduced 

 proportionately more than that of short-grasses by a drought period and is 

 correspondingly greater during a wet period (plate 70). 



The relation of grouping to palatabiUty is perhaps best seen in the mixed 

 prairie and true prairie, though it exists in all communities where two or more 

 dominants differ in this respect. In general, Stipa comata is most readily 

 eaten, Agropyrum glaucum slightly less so, and Andropogon scoparius little or 

 not at all, when they occur in mixture or as altemes. As a consequence, Stipa 

 is often eaten out or kept down to such an extent that it fails to fruit. In its 

 absence Agropyrum bears the brunt of the grazing and sooner or later decreases 

 to a marked degree, thus making the short-grasses more available. In spite of 

 their high value, the latter are less succulent and seem to be less palatable 

 during the growing season. It is only after Stipa and Agropyrum have dis- 



