OVERGRAZING. 297 



Causes. — The primary cause of overgrazing is stocking the range with more 

 animals than it can carry and still maintain its annual yield. This has been 

 the universal method by which the stockman has maintained a title to his 

 portion of the open range, since an overgrazed range offered little attraction 

 to a new-comer. Overstocking has become such a general practice through- 

 out the West, on private lands as well as upon the open range, that stockmen 

 have almost completely lost sight of the. potential carrying capacity of their 

 ranges. A corollary of this is the practice of year-long grazing or of grazing 

 during too long a season, with the result that the grass does not make a proper 

 growth in the spring or fails to ripen and drop its seeds in the fall. Trampling 

 is an inevitable concomitant of overstocking and frequently does more 

 damage than the actual grazing, especially in the vicinity of wells and tanks. 

 In addition, there are several important contributory causes of overgrazing. 

 The most important of these is the drought period of the climatic cycle. The 

 general practice of stockmen takes no account of the great variation in yield 

 between the dry and wet phases. The interval between them usually per- 

 mits the building up of the herd to the point where the range can not carry it 

 during the dry phase. For a year or more the range is destructively over- 

 grazed, until the herd is moved or a large portion has died. During such 

 drought periods as those of 1893-95 and 1916-18, the range may be so 

 damaged as to require several years to regain a fair carrying capacity and 

 many years to permit the development of its potential capacity. The effect 

 of rodents upon the range is essentially a matter of overstocking. A range 

 which is carrying thousands of prairie-dogs or jack-rabbits is in effect already 

 stocked with a considerable number of cattle. In the usual practice, however, 

 no allowance is made for this fact, and the rodents steadily increase the 

 damage done by the prevailing overstocking with cattle. This double effect 

 becomes most disastrous during the drought period and frequently results 

 in the complete destruction of the range over large areas, especially in the 

 Southwest. The effect of fire upon the range is relatively unimportant by 

 comparison, but it does sometimes do serious damage to the short-grass and 

 desert plains by killing the rootstocks, particularly during dry seasons or dry 

 years. 



Indicators of overgrazing — In grassland and scrub practically every species 

 may serve as an indicator of overgrazing. This is true also of herbs and shrub 

 associes, especially those of the subsere. In the case of woodland and forest 

 the dominants can act as indicators only in the seedling or sapling stage, but 

 the herbs and shrubs may indicate overgrazing as clearly as in other com- 

 munities. The primary basis of overgrazing indicators lies in the fact that 

 at any particular stage some species are eaten and others are not. Thus, at 

 any time the degree of overgrazing can be determined from both sets of 

 plants. The best method consists in using one set as positive indicators of 

 excessive grazing, and the other as a check upon these results; but in actual 

 practice the most convenient indicators are naturaly those that are not eaten. 

 In any community such relict indicators owe their importance in the first 

 place to the fact that the more palatable species are eaten down, thus render- 

 ing the uneaten ones more conspicuous. This quickly throws the advantage 

 in competition to the side of the latter. They receive an increasingly larger 

 share of water-content and light, and their growth increases accordingly. 



