GRAZING TYPES. 275 



of a particular region, pure consociations play an even smaller part on account 

 of their relatively small extent. While they are very helpful in ecological 

 analysis, they are of little importance in practical management. 



Local grazing types. — While the main grazing types, such as the formation 

 and association, indicate the comparative value of great regions, as well as 

 the groupings possible in any one> it is the local groupings which determine 

 the carrying capacity of a particular ranch and the proper system of manage- 

 ment to be employed upon it. For this reason, they may well be termed 

 practical grazing types. In areas relatively uniform, a single grazing type 

 composed of the two or three major dominants of the association may cover 

 a wide extent. This is the case with Stipa and Bouteloua in North Dakota 

 and Montana, Bulbilis, Agropyrum, and Bouteloua in the region of the Black 

 Hills, and Bulbilis and Bouteloua in Oklahoma and Texas. As a rule, how- 

 ever, changes in topography or soil or in the number and grouping of the 

 subdominants bring about important changes every few miles, and very 

 frequently adjoining sections will be found to have a different grouping or an 

 effective difference in relative abundance. Hence, it is clear that the local 

 community must determine the careful classification of the land section by 

 section, especially with reference to carrying capacity, as well as the method 

 of management. For example, while all the climax groupings in the mixed 

 prairie resemble each other in structure and treatment much more than they 

 do groupings of the true prairie or short-grass plains, they show decisive 

 differences among themselves. The carrying capacity and relation to over- 

 grazing of the Stipa- Bouteloua community differ from that of Agropyrum- 

 Bulbilis, and of both of these from that of Bulbilis- Agropyrum-Bouteloua. 

 The marked development of societies reduces the abundance of the dominant 

 grasses, and at the same time affects the carrying capacity. The relation 

 between the two effects depends upon the degree to which the subdominants 

 are grazed, but as a rule they are less palatable than the grasses. Over 

 regions of rolling topography, such as prairies and sandhills, the climax 

 groupings are regularly interrupted by valley and ridge communities which 

 are successional in nature. These are of relatively small extent and may fre- 

 quently occur with the climax grouping on a ranch of a section or less in 

 extent. In the case of the more level plains, the serai communities are con- 

 fined to stream valleys and breaks and cover much larger areas. They often 

 serve to mark the distinction between valley and upland ranches. They are 

 not confined to one association, but such a grouping as that of the Andropogons 

 may be found repeatedly from the true and mixed prairies through the short- 

 grass and desert plains. 



The number of such groupings is legion, and the most important occur 

 again and again in the region where they are characteristic. They have been 

 found in sequence over many thousands of miles in the West, and the most 

 frequent and important have been noted in connection with the frequence 

 and grouping of dominants under each association in Chapter IV. They are 

 of the first importance in determining local variations in grazing value and 

 are regarded as the basic indicators to be used in the range survey discussed 

 later. As already indicated, the major indication of the grouping must al- 

 ways be interpreted in connection with the minor indication of the societies 

 present. In its application to grazing at least, the grouping is so important 



