14 BULLETIN 738, U. S. DEPARTMENT OF AGRICULTURE. 



After seedlings are 6 inches high the damage caused by moderately 

 close grazing is negligible. According to Table 5, western yellow 

 pine reaches this height in 5 years on the better sites or in 8 years on 

 the poorer sites, Douglas fir in from 10 to 12 years, and lodgepole 

 pine in 9 years. There is practically no damage at all after seedlings 

 reach 1.5 feet in height, or after from 13 to 17 years for western yellow 

 pine, from 16 to 20 years for Douglas fir, and 16 years for lodgepole 

 pine. 



From Table 3 and the height growth it is computed that on the 

 Deadwood allotment 46.5 per cent of the western yellow pine which 

 germinates will be killed if the area is grazed every year, or 8.7 per 

 cent if grazing is eliminated until seedlings have passed their third 

 year. On the South Fork the figures will be 43.4 per cent and 5.7 

 per cent. Of Douglas fir in Deadwood, 48.8 per cent will be killed 

 by grazing every year, or 14.3 per cent if it is suspended for three 

 years; on the South Fork 44.2 per cent, or 9.9 per cent after three 

 years, will be lost. In Deadwood 39.7 per cent of the lodgepole pine 

 seedlings will be killed, or 15.1 per cent if the area is grazed after the 

 third year only. 



According to Table 3 a much larger proportion of western yellow 

 pine seedlings less than a year old are killed than of Douglas fir, 

 while only half as many of lodgepole pine are killed. This is probably 

 due partly to the taller and more succulent and brittle stems of western 

 yellow pine seedlings and partly to the fact that lodgepole pine repro- 

 duction is more abundant where there is comparatively little palatable 

 forage cover, so that grazing is apt to be lighter on spots where 

 lodgepole pine seedlings predominate than where western yellow 

 pine is the prevailing species. The characteristic distribution of 

 western yellow pine seedlings in clumps planted by chipmunks and 

 mice (Douglas fir and lodgepole pine usually occurring singly) may also 

 result in a somewhat larger mortality, since the disturbance which 

 affects one seedling in a clump affects the whole group. 



Table 8 indicates that as a general thing western yellow pine is 

 less likely to be killed after its third year than is Dougtets fir or lodge- 

 pole pine. This may be due to the larger size of three-year old yellow 

 pine seedlings. 



SEASON OF INJURY. 



To determine the relation between the amount of damage and the 

 time of year when the grazing was done, the plots grazed on the Dead- 

 wood allotment in 1913 were grouped into three classes: (a) those 

 grazed early in the season, or up to the latter part of July, which in 

 1913 was a fairly moist period; (b) those grazed in midseason, from 

 late in July to the middle of August; and (c) those grazed late, or 

 after the middle of August, the driest part of the season. Table 6 

 shows the relative amount of damage done during each period. 



