EFFECT OF* GRAZING ON WESTERN YELLOW PINE. 



15 



Table 6. —Grazing, injuries, by time of year, in percentages of number of seedlings on the 

 plots at the time they were grazed'. 



(Deadwood allotment, 1913.) 





Injured (over 1 year 

 old). 



Killed. 



Time of grazing and species. 



Browsed. 



Trampled. 



Under 1 

 year old. 



Over 1 year 

 old and 

 under \\ 

 feet high. 



Early summer: 



0) 



0) 

 (0 





24.2 

 20.6 

 18.5 



0.5 







.8 







4.8 









All 



.1 





23.4 



1.4 









Middle summer: 



0) 



C 1 ) 





14.3 



24.7 

 6.8 



.5 





C 1 ) 



C 1 ) 



1.4 





1.5 







All 



.6 



.2 



11.6 



1.1 







Late summer: 



0) 

 C 1 ) 



C 1 ) 





6.7 

 8.9 

 9.3 







C 1 ) 



C 1 ) 





Lodgepole pine 



2.0 



All 



.5 



.1 



8.0 



.5 



1 Very small. 



Injuries which did not result in death, particularly those due to 

 browsing, though insignificant at any season, were greater late in the 

 season than during the earlier period. This is probably due to the 

 drying of the succulent forage of the early part of the season and to 

 the greater liking of sheep for browse types of forage as the season 

 advances. 



The proportion of seedlings killed by grazing, particularly of those 

 less than a year old, was very much greater early in the season than 

 it was later. The reasons for this are that early in summer the seed- 

 lings are rather brittle, with little wood in their stems ; their roots do 

 not go down very deep; the soil is moist and easily shoved out of 

 place by the sheep; and seedlings injured early are either killed out- 

 right or have small chance to recover because of the dry period which 

 follows the injury. By the middle of August the season's growth is 

 nearly completed, the stems are tougher, the roots deeper and more 

 widely spread, the soil is more firmly packed, and an injury is soon 

 followed by the fall rainy period and the long winter period of rest, 

 so that there is a fair chance for recovery from slight disturbance. 



RELATION BETWEEN AMOUNT OF DAMAGE AND INTENSITY OF GRAZING. 



The relation between intensity of grazing and amount of damage is 

 shown in Table 7. Where the surface of the ground was not appre- 

 ciably disturbed by trampling and very little of the forage cover was 

 eaten the plot was classed as "lightly grazed" ; where most of the 



