EFFECT OF GRAZING ON' WESTERN YELLOW PINE. 19 



RELATION BETWEEN AMOUNT OF DAMAGE AND AMOUNT AND CHARACTER OF THE 



FORAGE. 



The quantity of palatable forage on a given area may affect the 

 amount of damage done in two ways. If the total quantity of feed 

 is too small for the number of stock allotted to the area, there will 

 probably be considerable browsing injury and more injury from 

 trampling than if there is abundant feed so that the sheep need not 

 wander around looking for it. On the other hand, whether the 

 allotment as a whole has ample forage for the allotted stock or not, 

 the injury due to trampling, which causes most of the deaths of small 

 seedlings, is likely to be greatest on those parts of the allotment 

 where the amount of palatable forage is greatest. The reason for 

 this is that the sheep will spend more time where forage is abundant 

 than where it is scanty. 



Trampling is more serious on steep slopes than on more level 

 places, except around beds, watering places, or along driveways, 

 because of the tendency of sheep on hillsides to follow each other's 

 footsteps and thus wear trails, and because of the greater likelihood 

 that seedlings will be uprooted or buried by trampling in such places. 



Where the forage is composed largely of tender herbaceous vege- 

 tation reproduction is more subject to damage than where there 

 are shrubs or dense tufts of perennial grasses or weeds to protect the 

 seedlings. 



COMPARISON OF THE DAMAGE CAUSED BY SHEEP AND BY OTHER AGENCIES. 



To account for deaths due directly or indirectly to grazing, but 

 whose cause could not be definitely traced, a comparison was made 

 between the total deaths during the summer on grazed and ungrazed 

 plots. 



With very few exceptions, the mortality on grazed plots was the 

 greater for all species and size classes. Excepting the 2 to 3 year 

 old white fir, for which there were too few figures for a good average, 

 this difference in favor of ungrazed plots was very marked for all 

 seedlings less than 6 inches high. 



Table 10 indicates that a large number of the smaller seedlings 

 died even where no grazing was done. The total amount of injury 

 and death during the period of the study due to causes other than 

 grazing is summarized in Table 11. Tables 12 and 13 compare graz- 

 ing injuries with those due to other causes for the different species 

 and allotments. 



The increase in the number of deaths in 1913 and 1914 was due to 

 the greater number of plots and the larger number of seedlings 

 examined, and to the greater proportion of seedlings less than 1 

 year old which resulted from the abundant germination, especially 

 in 1913. 



