EFFECT OF GRAZING ON WESTERN YELLOW PINE. 



19 



average growth of 0.7 foot for the three-year period, 1912-1914. 

 Measurements of a similar number of trees growing in the check 

 plots just outside these fenced areas showed an average height growth 

 of 0.2 foot for the three-year period. 



The rate of growth of 46 badly grazed saplings at Fort Valley, 9 

 miles northwest of Flagstaff, and 59 uninjured saplings of the same 

 age in a pasture on Observatory Hill, just outside of Flagstaff, the 

 two sites being very similar, are given in Table VIII. 



Table VIII. — Comparative growth of trees in pasture and on overgrazed range. 



Location. 



Number 

 of trees. 



Average 

 age. 



Average 

 height. 



Average 

 annual 

 growth. 



Iu pasture 



Overgrazed range . 



46 



Years. 

 17.2 

 17.0 



Feet. 

 5.2 

 2.1 



Feet. 

 0.36 

 .12 



The foregoing comparisons, which are believed to be representa- 

 tive, indicate that grazing injuries decrease the rate of growth of 

 young trees from one-half to two-thirds. 



From the standpoint of the production of a crop of timber this 

 check in the growth of reproduction is. not a serious matter, provided 

 the trees have a chance to outgrow the injuries before their vitality 

 is destroyed. The addition of 20 or 30 years to the period of rota- 

 tion is not in itself a vital consideration in the management of yel- 

 low pine. Retarded growth is a serious matter, however, when it 

 is considered that grazing conditions are generally stable and that 

 where severe damage occurs the trees have no opportunity to out- 

 grow their injuries, but are slowly killed. 



FORM OF TREE. 



It is generally thought that the bole of a young tree that is severely 

 injured is likely to become crooked or forked. This belief appears 

 to have little basis in fact. The probable cause of crooked boles in 

 nearly all instances is that the trees have at some time been over- 

 topped or suppressed and in that condition have grown at an angle 

 toward the strongest light, later becoming dominant or codominant 

 and attempting to grow upright. Forked boles serious enough to be 

 objectionable are formed at a height above that affected by grazing. 

 Observations of a great many young trees recovering from severe 

 injuries revealed no deformities that promised to be at all prominent 

 when the trees mature. Nearly all grazing injuries occur at a height 

 of less than lr| feet, and the trees, when protected, very quickly de- 

 velop a leader which gradually outstrips all others. The laterals of 



