PLANT SUCCESSIOlSr AND KANGE MAISTAGEMEKT. 65 



SUMMARY OF THE EFFECT OF GRAZING ON PLANT SUCCESSION 



ON THE RANGE. 



Grazing may cause either progressive or retrogressive succession, 

 depending chiefly upon the closeness with which the herbage is 

 grazed annually and the time when it is cropped. If the forage crop 

 is grazed closely before seed maturity each year, the general trend 

 of the succesion will be retrogressive ; if, on the other hand, the crop 

 is maintained in a high state of vigor at all times and then grazed 

 after seed maturity every third or fourth year or so, the succession 

 will be progressive, or, if there is virtuall}^ a full ground cover, a 

 maximum density will be maintained. Premature and too close graz- 

 ing not only favor retrogressive succession and ultimately the de- 

 struction of the vegetative cover, but also tend to impair the fertility 

 of the soil through the devastating effect of erosion. The seriousness 

 of the depletion of the soil, provided the lands are judiciously man- 

 aged, will determine chiefly the time required for thorough revegeta- 

 lion. Therefore, the longer retrogressive succession is permitted to 

 operate the longer will be the time required for the reestablishment 

 of the forage cover. The final outcome of vegetative degeneration 

 and erosion is the translocation of the entire soil formation and the 

 exposure of the underljdng rocks. As a rule, however, only the rich 

 surface layer of soil is removed, a condition which favors the im- 

 mediate establishment of a cover of the first-weed-stage plants. 



The continued hard use of established live-stock driveways and 

 bed grounds favors the destruction of the more stable type of vegeta- 

 tion and the establishment of plants of the early and late weed 

 stages. These species afford highlj^ reliable indicators of overgraz- 

 ing and thus show clearly what lands are being depleted or soon will 

 be in an inferior state of productivity provided the disturbing factor 

 is not corrected. Obviously, therefore, the use of established drive- 

 ways and bed grounds, especially the latter, tends greatly to decrease 

 the carrying capacity of the lands. 



Owing to the hard packing of the soil, these much trampled areas 

 revegetate slowly. The succession on bed grounds, for instance, is 

 similar to that on depleted lands, the revegetation beginning with 

 the early- weed stage and progressing through the intermediate covers 

 to the subclimax. 



In the way of revegetation, it is evident that yearlong protection 

 of bed grounds and other depleted lands from live stock tends to 

 hasten vegetative or asexual reproduction no more than when the 

 grazing is deferred until after seed maturity. Deferred grazing, on 

 the other hand, has the additional distinct advantage over yearlong 

 protection of permitting the forage crop to be grazed during the re- 

 stocking period, and of procuring a maximum stand of seedling 

 112655°— Bull. 791—19 5 



