2o6 GRAZING ON WOODLANDS 



eat also the leafage and tender twigs of the aspen. Thus the 

 oncoming aspen stand is often badly injured or even killed by- 

 grazing animals. This situation usually makes it very difficult 

 to secure a succeeding stand of timber on cut-over lands without 

 some loss in forage utilization. 



Effects of Sheep Browsing. — For a period of five years Samp- 

 son^ made an exhaustive study of the effects of sheep and cattle 

 grazing upon the reproduction of aspen under typical range con- 

 ditions. It was found that 27.2 per cent of the aspen repro- 

 duction under about 40 inches in height was killed by light sheep 

 grazing, 31.8 per cent on moderately grazed areas, and 65 per cent 

 on lands closely cropped. One of the silvicultural practices is to 

 clear-cut the aspen stand. Under average conditions where such 

 cutting is done, a dense stand of root sprouts invariably replaces 

 the original cover after the first year of cutting. On clear-cut 

 plots especially established for the grazing study, the damage 

 done by sheep browsing was found to be exceedingly heavy. 

 Three successive years of sheep browsing on clear-cut plots re- 

 sulted in the complete destruction of the young aspen stand. In 

 other words, at the end of the third year of removal of the sprouts 

 by sheep, the sprouting ceased completely, and the aspen roots 

 were evidently exhausted and died (Figs. 68 and 69). It was 

 concluded that under moderate conditions of grazing, when the 

 sprouts reach a height of about 45 inches, they are practically 

 exempt from injury by sheep browsing. The extent to which 

 the aspen sprouts in standing timber were either killed or injured 

 was found to be in direct proportion to the intensity of the 

 grazing. Although the leaves of the young stand were most 

 relished, the stems, as shown in Figure 70, were nevertheless 

 devoured to a considerable extent. A goodly portion of the 

 young tender twigs was also consumed by sheep in the autumn 

 after the leaves had dropped. 



Effects of Cattle Browsing. — The injury to the aspen stand 

 caused by the grazing of cattle, although a factor of some im- 

 portance in obtaining good thrifty reproduction, was in no sense 



' Sampson, Arthur W., "Effect of Grazing upon Asoen Reproduction." U. S. 

 Dept. of Agr. Bui. 741, 1919. 



