272 GRAZING INDICATORS. 



best system will necessarily employ both, but the vast extent of the climaxes 

 and their obvious dependence upon the vegetation-form suggests them as the 

 preferred basis. This has the further advantage of making the practical and 

 the ecological system the same and of avoiding the confusion which exists in 

 forestry, where the practical types and ecological units are often wholly 

 different. The developmental method is also desirable in that it furnishes a 

 uniform method of dealing with fin6r and finer divisions upon the basis of 

 climate, soil, and region, as well as upon that of ecology and floristic. As all 

 of these enter into practice sooner or later, it seems clear that the best treat- 

 ment of grazing indicators is that which relates them to the proper formation 

 and association. In consequence, the following discussion deals first with 

 climax communities as indicators as much the most important, and then with 

 the more localized serai communities. In addition, some account is taken of 

 artificial communities due to planting or other modification, since it is assumed 

 that these will play an increasingly larger part in the grazing industry of the 

 future (plate 64). 



Significance of climax types. The value of the climax community as an 

 indicator rests primarily upon the characteristic life-form. This is clearly 

 seen in the three types, grass, weeds, and browse, but in the case of forest 

 it depends upon the life-forms of the layers and serai stages. Climax forma- 

 tions are far more extensive than the developmental stages which occur here 

 and there in them. Moreover, such stages are constantly moving toward 

 the climax condition, slowly in the case of priseres and rapidly in the case 

 of subseres. The climax communities are extensive and permanent, the serai 

 ones local and temporary as a rule. As a consequence, the grazing practice 

 of large regions must be based upon the indications of the climax formation or 

 its subdivisions, while in a particular locality the importance of certain serai 

 communities may demand some modification in practice. Apart from the 

 vegetation-form as shown in grass, herb, shrub, or tree, the habitat-form and 

 growth-form of the dominants must also be taken into account. Communi- 

 ties of sod-forming grasses indicate different values and treatment than those 

 of bunch-grasses, while there is a striking difference between the associations 

 of taU-grasses and of short-grasses. Climax communities of dominant herbs 

 do not exist, but prairie and alpine meadow often contain so many mixed 

 societies that the grazing value depends largely upon them. The indications 

 of shrubs vary with the deciduous or evergreen nature of the leaf, succulence, 

 form, ability to make root-sprouts, fruit, etc. The dominant trees of climax 

 forest enter the question of grazing very little if at all, and the grazing type of 

 each forest is determined by the greater abundance of grass, weeds, or browse. 

 Finally, the grazing value of a community, and hence its indicator meaning, 

 depend greatly upon whether it is pure or mixed. This is partly a matter of 

 the relative value of the dominants as forage, and partly of the degree to 

 which each is grazed and of its ability to grow and reproduce under the existing 

 conditions. Mixed communities greatly predominate, and their utilization 

 is determined to a large degree by the kind of mixture. They may consist 

 almost wholly of dominants of the same vegetation-form, such as the short- 

 grasses of the Bulbilis-Bouteloua plains, or they may contain shrubs and 

 grasses, as in savannah. In addition, grassland which exhibits a marked 

 development of societies is essentially a mixed community with respect to 

 grazing, since it permits selection by cattle or sheep, or mixed grazing by both. 



