EFFECT' OF GRAZING UPON ASPEN" REPRODUCTION. 3 



season, the plots in the standing timber being examined only in the 

 autumn. 



The reproduction injured or killed was classified according to 

 height, sprouts of from about 6 inches to 1| feet constituting the 

 youngest class, those from 1| to 2\ feet the second class, and so on 

 up to sprouts 4^ feet high. Record was also made of the intensity 

 of grazing; that is, whether it was light, medium, or heavy. Plots 

 were classed as "lightly grazed" where 50 per cent or less of the 

 palatable vegetation had been cropped, "moderately grazed" where 

 from 50 to 70 per cent of the forage had been consumed, and "heav- 

 ily grazed" where more than 75 per cent of the palatable vegetation 

 had been eaten. 



INJURY TO ASPEN REPRODUCTION BY LIVE STOCK IN STANDING 



TIMBER. 



EFFECT OF SHEEP BROWSING. 



Injurious browsing of aspen reproduction means the removal by 

 stock of terminal or lateral shoots, or both, to a sufficient extent to 

 interfere more or less seriously with the subsequent growth and 

 development of the sprouts. The removal of a single lateral twig 

 or the mere nipping of the terminal bud are disregarded, since the 

 study has shown that -to interfere seriously with the food manu- 

 facturing power or with the form development of the young trees 

 at least one-fourth of the total number of branches must be destroyed. 

 If browsing is confined to the upper hah of the sprout, including the 

 terminal shoot, the damage is more serious, especially so far as 

 concerns the ultimate form of the tree. 



Table 1 summarizes the effects of sheep browsing on plots in standing 

 timber, according to seasons and to the intensity of grazing. There 

 is also given the number of sprouts injured by other things than 

 five stock. Of a total of 16,631 sprouts observed during the five years 

 of study, 17.1 per cent were killed and 27.3 per cent were more or 

 less injured by browsing, while 37.5 per cent were uninjured. It is 

 noteworthy that 11.7 per cent of the total number of sprouts were 

 killed and 6.3 per cent injured by causes other than grazing. Un- 

 favorable climatic conditions and the activities of bark-eating 

 rodents were chiefly responsible for these results. It is evident that 

 very few vigorous sprouts remain to perpetuate the stand where 

 sheep grazing is continued. 



Considerable variation in extent of injury to the reproduction 

 occurs in different seasons. In the case of the lightly grazed plots, 

 for example, only 3.7 per cent of the aspen reproduction was injured 

 in 1912, but the percentage was 30.8 in 1913. Similar variations 

 occur in the case of moderately grazed and heavily grazed plots. 



