4 BULLETIN 141, IT. S. DEPARTMENT OF AGRICULTURE. 
They are probably due more or less to chance. Xo appreciable 
difference was observed in the extent and degree of injury by browsing 
during different portions of the season so long as the foliage remained 
intact. When the wood of the stems hardens the stems are browsed 
practically not at all by cattle and only to a limited extent by sheep. 
The effect of the intensity of grazing on the Vigor and growth of 
the reproduction is better shown by figures covering a number of 
years. These are given in Table 2, which summarizes the data on 
intensity of grazing presented in Table 1 . 
The lighter the grazing the greater is the percentage of uninjured 
sprouts. Thus, on the lightly grazed plots more than hah (58.2 
per cent) of the total number observed were udiinjured; on the 
moderately grazed plots a little less than half (43.8 per cent); and 
on the heavily grazed areas only about a fifth of the stand (22.2 per 
cent) escaped injury. 
Table 1. — Injury to aspen sprouts on plots in standing timber. 
Grazing intensity and year of 
examination. 
Total 
number 
of 
sprouts. 
Uninjured 
sprouts. 
Killed by 
grazing. 
Injured by 
grazing. 
Sprouts 
killed by 
causes other 
than graz- 
ing. 
Sprouts in- 
jured by 
causes other 
than graz- 
ing. 
Lightly grazed: 
1912 
108 
954 
1,169 
595 
267 
128 
880 
2,697 
1.864 
1,127 
154 
458 
2,471 
2,6-32 
1,127 
Num- 
ber. 
104 
633 
6-52 
233 
176 
117 
617 
1,011 
'571 
611 
138 
234 
624 
370 
151 
Per 
cent. 
96.3 
66.3 
55.7 
39.1 
65.9 
91.4 
70.1 
37.5 
30.6 
54.2 
89.6 
51.3 
25.2 
14.0 
13.4 
Num- 
ber. 
""a" 
89 
95 
36 
Per 
cent. 
"2.2 
7.6 
15.9 
13.5 
Num- 
ber. 
4 
294 
219 
41 
40 
5 
252 
532 
227 
310 
3 
22-3 
1,192 
964 
239 
Per 
cent. 
3.7 
30.8 
18.7 
6.9 
15.0 
3.9 
Num- 
ber. 
Per 
cent. 
Nu 772- 
ber. 
Per 
cent. 
1913 
1914 
1915 
1916 
Moderately grazed: 
1912 
1913 
28.6 
1914 
303 
327 
146 
9 
11.2 
17.5 
12.9 
5.8 
19.7 
1915 
12.1 
27.6 
1.9 
48.7 
48.3 
36.6 
21.2 
1916 
Heavily grazed: 
1912 
1913 
1914 
412 
688 
712 
16.7 
25.1 
63.2 
1915 
1916 
Total 
16,631 
6.242 
[2,838 
37.5 
■i,T 
4,545 
1.449 
27.3 
'till 
1,057 
6.3 
Table 2. — Injured, killed, and uninjured aspen sprouts on plots in standing timber 
subject to sheep grazing during a five-year period. 
Period of examinations and 
grazing intensity. 
Total 
number 
of 
sprouts 
ex- 
amined. 
Uninjured 
sprouts. 
Sprouts killed 
by grazing. 
Sprouts injured 
by grazing. 
1912-1916: 
Lightly grazed 
Moderately grazed 
Heavily grazed... 
3.093 
6! 696 
6',S42 
Num- 
ber. 
1,798 
2.927 
1,517 
Per 
cent. 
58.2 
43.8 
22.2 
Num- 
Per 
Num- 
ber. 
cent. 
ber. 
241 
7.8 
598 
776 
11.6 
1,352 
1.821 
26.6 
2,621 
Per 
cent. 
19.4 
20.2 
38.4 
