12 



BULLETIN 738, U. Si DEPARTMENT OF AGRICULTURE. 



SIZES INJURED. 



Table 2 shows the total amount of injury done by sheep on all the 

 sample plots during the period of the study, classified according to 

 the size of seedlings injured. Of the 1,782 seedlings killed, 1,294, or 

 73 per cent, were less than a year old, while only 11, or about one- 

 half of 1 per cent, were over 6 inches in height. Only one seedling 

 over 18 inches high was killed by sheep during the three years. 

 Only one sapling over 3.5 feet high was browsed or trampled; most 

 of the injuries from browsing or trampling were confined to seedlings 

 less than 1.5 feet in height. 



The relative mortality of seedlings of different sizes is shown in 

 Table 3. During the first few years seedlings succumb very easily 

 to slight injuries, because of their small size, shallow root system, 

 and the lack of woody matter in their stems. The loss due to grazing 

 decreased from about 20 per cent for seedlings in their first year to 

 11 per cent for those in their second and third years. By the end of 

 the third year they are from 2 to 4 inches high (depending on species 

 and site), their stems have become woody and fairly tough, and their 

 roots penetrate the soil for a foot or more, so that they are not easily 

 uprooted by trampling nor exposed to drying by the loosening of the 

 soil. Injury from grazing is so slight after this that there is no need 

 for closing reproduction areas to sheep after the third year, though it 

 may be desirable to graze such areas lightly for a few years more, 

 until the seedlings reach a height of 6 inches. 



Table 2. — Relation between size of seedlings and injury by grazing. 

 (Total injuries for three years on sample plots on all allotments.) 



Species and height class. 



Injured. 



Need- 

 les. 



Side 

 branches 



Leader. 



Bark. 



Tram- 

 pled. 



All. 



Killed. 



Western yellow pine: 



Under 1 year 



1 year old to 6 inches high . 



6 inches to li feet 



H to 21 feet.". 



2* to 3* feet 



Douglas fir: 



tinder 1 year 



1 year old to 6 inches high . 



6 inches to 14- feet 



14; feet to 24 feet 



2i to 31 feet 



Lodgepole pine: 



Under 1 year ......' 



1 year old to 6 inches high . 



6 inches to 14; feet 



H- to 24- feet 



2J to 34 feet 



3* to 44; feet 



White fir: 



Under 1 year 



1 year old to 6 inches high . 



Ill 



1.010 

 216 



28 



1 



4 





3 



150 



18 



124 



22 



1 



5 





4 





2 



126 



8 



128 



13 



2 



4 





3 





1 





