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 1J feet constituting the 
youngest class, those from 1J to 2 J feet the second class, and so on 
up to sprouts 4J 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 half 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. 
