4 BULLETIN 741, U. S. DEPARTMENT OF AGRICULTURE. 



They are probably due more or less to chance. No 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 half (58.2 

 per cent) of the total number observed were uninjured; on the 

 moderately grazed plots a littlte 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 



2,632 



1,127 



Num- 

 ber. 

 104 

 633 

 652 

 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. 



Per 

 cent. 



Num- 

 ber. 

 4 

 294 

 219 

 41 

 40 



5 

 252 

 532 

 227 

 310 



3 



223 



1,192 



964 



239 



Per 

 cent. 



3.7 

 30.8 

 18.7 



6.9 

 15.0 



3.9 

 28.6 

 19.7 

 12.1 

 27.6 



1.9 

 48.7 

 48.3 

 36.6 

 21.2 



Num- 

 ber. 



Per 



cent. 



Num- 

 ber. 



Per 

 cent. 



1913 



21 

 89 

 95 

 36 



2.2 



7.6 



15.9 



13.5 











1914 











1915 











1916 











Moderately grazed: 



1912 











1913 



303 

 327 

 146 



9 



11.2 

 17.5 

 12.9 



5.8 











1914 











1915 











1916 











Heavily grazed: 



1912 











1913 











1914 



412 

 688 

 712 



16.7 

 26.1 

 63.2 











1915 











1916 





















Total 



16,631 



6,242 



37.5 



2,838 



17.1 



4, 545 



27.3 



1,449 



11.7 



1,057 







6.3 











Table 2. — Injured, hilled, and uninjured aspen sprouts on plots in standing timber 

 subject to sheep grazing during a Jive-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 

 6,842 



Num- 

 ber. 

 1,798 

 2,927 

 1,517 



Per 



cent. 



58.2 

 43.8 

 22.2 



Num- 

 ber. 

 241 

 776 



1,821 



Per 



cent. 



7.8 



11.6 



26.6 



Num- 

 ber. 



598 

 1,352 

 2,621 



Per 



cent. 

 19.4 

 20.2 

 38.4 



