

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 7 



AMOUNT OF DAMAGE. 



Table 1 shows the kind and amount of damage done by sheep on 

 the different allotments during the course of the study. 



The damage to seedlings more than a year old was negligible in 

 quantity; a yearly average of 1.9 per cent of the number on grazed 

 plots was killed on the Deadwood area, and 3.7 per cent on the 

 Silver Creek area. The one year's record for the South Fork (4.7) 

 indicates, when compared with the same year's record on the other 

 allotments, that the yearly average for a three-year period would 

 probably have been between the Deadwood and Silver Creek averages. 

 Of seedlings less than one year old, on Deadwood an average of 15.4 

 per cent were killed, and on Silver Creek 24.9 per cent. The greater 

 mortality of both classes of seedlings on the Silver Creek area was 

 due partly to the greater intensity of grazing on that allotment and 

 partly to differences in the relative distribution of ages; the Silver 

 Creek area had a much larger proportion of reproduction less than 

 10 years old. These figures show the proportion of damage on 

 grazed plots alone; that is, they indicate the maximum loss which 

 would result if the sheep grazed over every square yard of their 

 allotment. As a matter of fact an area is seldom grazed, so closely 

 unless it is very much overstocked; a great many spots are missed, 

 and many of them are likely to be patches of reproduction, since 

 there is usually little palatable forage in such places. 



The last columns in Table 1 show the proportion of injury to the 

 total number of seedlings on all of the plots on each allotment. On 

 the Deadwood area, which was grazed rather lightly, averages of 1.1 

 per cent of the older seedlings and 8.8 per cent of those less than a 

 year old were killed each year, while on the closely grazed Silver 

 Creek area 2.5 per cent and 14.8 per cent, respectively, were killed. 



Of the older seedlings on grazed plots on Deadwood but 0.7 per 

 cent were browsed, and of those on Silver Creek 1.5 per cent. Con- 

 sidering all plots whether grazed or not, 0.4 per cent of the seedlings 

 on Deadwood and 1.1 per cent of those on Silver Creek were browsed 

 each year; and fully one-third of these "injuries" consisted of slight 

 browsing of needles or tips of lateral branches only. The smaller 

 proportion of one-year seedlings classed as "injured" is due to the 

 fact that they are usually killed if injured at all. 



Of the three important species present, western yellow pine appears 

 to be most liable to browsing injury, lodgepole pine somewhat less 

 so, and Douglas fir least. White fir is practically never browsed. 



