278 GRAZING INDICATORS. 



Savannah has to do with the relations of two contiguous climaxes, and park 

 with that of a subclimax to its climax. The former is a permanent condition, 

 varying more or less under the influence of the wet and dry phases of climatic 

 cycles, while the latter is usually a temporary community, occupying its 

 proper place in prisere or subsere, and passing ultimately into the climax. 

 Hence, the indicator values of different types of parks are dealt with in the 

 next section, while those of savannah are considered here. True savannah 

 has value as an indicator of climate as well as of practice. It not only 

 indicates a transition between the climates of the respective climaxes, but 

 also serves to record the course of the climatic cycle. The amount to which 

 it increases its area and density under the same conditions is a measure of the 

 effect of the wet phase, and the dying-out of individuals, of the dry phase. 

 Such measurements are possible only under control, however, owing to the 

 almost universal disturbance of fire or overgrazing. 



Kinds of savannah. — With reference to practice, savannah indicates the 

 general possibility of agriculture. For the most part, this is of the dry- 

 farming type, though in central Texas it indicates humid or subhumid farm- 

 ing, and in California farming by means of drought-evasion. With respect 

 to grazing, the indications of savannah depend primarily upon the grass 

 dominants. In fact, the indicator value of savannah is essentially that of 

 the grassland community, unless the trees or shrubs are sufficiently close to 

 reduce materially the amount of grass. When the shrubs themselves have 

 distinct value as browse, the carrying capacity becomes greater than that of 

 the grassland alone, and mixed grazing is also favored. The yellow pine 

 savannah of the Black Hills and eastern Rocky Mountain region occurs in 

 the mixed prairie, while in the Southwest it lies in the short-grass association. 

 In both cases, the grazing value of the grassland is practically unchanged, 

 except for some reduction in cover just beneath the trees. Pine savannah 

 also occurs along the upper edge of the bunch-grass prairie, but it is rarely 

 extensive here. Cedar savannah is found chiefly in the short-grass com- 

 munity, but is frequent also in the desert plains and mixed prairies. Where 

 the cedar is low, it materially reduces the total carrying capacity, though this 

 is often offset by the presence of browse shrubs. Mesquite savannah lies 

 typically in the desert plains, though the mesquite itself extends northward 

 into the short-grass association of the Staked Plains. The shrubs have little 

 effect upon the amount of grass, and they change the indications of the com- 

 munity only to the extent that they are valuable for browse. Toward the 

 lower edge of the savannah the shrubs become denser as they pass into the 

 desert scrub, and the grassland rapidly decreases to the point of disappearance. 

 Oak savannah may be of the tree or shrub type. The latter is most typical 

 on the plateaus and mountain ranges of southwestern Texas, New Mexico, 

 Arizona, and Mexico, where it is formed chiefly by live-oaks. It lies in the 

 desert plains grassland, or in the Andropogon zone just above. The grazing 

 value due to the grasses is greatly increased by the abundant browse, and 

 such savannah may well be regarded as one of the best of all grazing types, 

 owing to the assurance it gives against drought in connection with mixed 

 grazing. Tree savannah consisting of oaks usually has little or no browse 

 value, and its indication is essentially that of the grass community in which 

 it is found, with some reduction caused by shading. In California, the 



