274 GRAZING INDICATORS. 



as well, and that economic considerations give them greater significance in 

 this role. Our knowledge of the Pacific alpine meadow is too small to enable 

 us to draw an accurate comparison with the Petran association. They are so 

 nearly alike in the growth-form and genera of the dominants and in the 

 number and luxuriance of the societies that they exhibit no clear difference 

 in yield per unit area. In spite of this, the Petran association is actually 

 very much more important, for it covers an area many times greater, is more 

 coherent, and for the most part covered by snow to a less degree and for a 

 shorter period. 



The grazing value of the chaparral associations depends largely upon the 

 presence of oak, which is usually the most important of the dominants for 

 browse. For this reason, the Petran chaparral is usually more important 

 than the Coastal, though its value decreases greatly with the dropping out 

 of the oak to the northward, just as it increases to the southeast with a larger 

 number of species of Quercus. In the sagebrush formation, the Basin associ- 

 ation is all-important, the Coastal community being of relatively small extent 

 and containing but one or two dominants of value. The differences between 

 the associations of the desert scrub are not so clear-cut, but the advantage 

 lies in general with the western community, owing largely to the much greater 

 number of succulents. The three associations of the woodland exhibit a 

 thin ground cover of grass and shrubs, resulting from the combined effect of 

 dryness and shade. They produce savannah where they are in contact with 

 grassland or scrub, and in such cases possess more or less of the grazing value 

 of the latter. The presence of oak gives woodland some value as browse, 

 and in this respect the oak-cedar community stands first and the pine-oak 

 next. The montane associations differ strikingly in ground cover, the Petran 

 having the herbaceous layers best developed, and the Sierran, the shrub 

 layer or so-called subclimax chaparral. The former has usually the greater 

 importance for grazing, since many of the shrubs of the chaparral are un- 

 palatable. The comparative value of the associations of the subalpine forest 

 is less certain, but on the whole the Petran has the advantage, especially 

 when the serai grasslands are taken into account. 



Consociations as indicators. — The value of the consociation as an indica- 

 tor is determined primarily by the life-form. Grassland derives its unique 

 importance for grazing from the grass dominants, while the value of scrub 

 dominants is much lower and more variable, and that of forest consociations 

 almost wholly dependent upon the undergrowth. In the grassland the chief 

 value lies in the consociation, with the scrub in the consociation and its socie- 

 ties, and in the forest it lies in the shrub and herb societies alone. Moreover, 

 grass consociations are true grazing types, scrub are primarily browse types, 

 and forest and woodland are grazing or browse, depending upon the relative 

 abundance of herbs and shrubs. Consociations may be pure or mixed, and 

 the indicator meaning naturally varies accordingly. While mixed communi- 

 ties are the rule, pure consociations are sufficiently frequent to permit the 

 determination of carrying capacity, response to overgrazing, and other fea- 

 tures which make up the total grazing value. In the case of mixed communi- 

 ties the analysis is based upon the normal response of each pure consociation, 

 modified by their varying relations to the grazing animals and their com- 

 petitive reactions upon each other. In dealing with the actual grazing types 



