EFFECT OF GRAZING ON WESTERN YELLOW PINE. 21 



Table IX. — Comparative growth of protected and unprotected saplings. 



Height classes. 



Average growth 

 during 3 years. 



In 



pastures. 



Outside 



of 

 pastures. 



Feet. 



1 



Feet. 

 0.8 

 1.1 

 1.2 

 1.4 



Feet. ' 

 0.2 

 .3 



.4 

 .4 



2 



3 



4 : 



Average 



1.1 



.32 



The results show that the growth of the protected saplings is more 

 than three times as rapid as that of the unprotected ones and indi- 

 cate a marked ability of young pines when protected to recover from 

 injuries. This conclusion is substantiated by the results of measure- 

 ments of trees previously injured within the fenced plots and of 

 trees outside subject to continued injury (p. 18). As stated in that 

 case, the ratio of growth between protected and unprotected trees 

 was as 7 to 2. 



Even though protection against severe grazing may enable seri- 

 ously injured saplings to recover, such protection may not be advis- 

 able unless the loss of young trees on unprotected areas is excessive. 

 Reference to Table I shows that an average of only 0.9 per cent of 

 the total number of trees were found dead during the three years 

 covered by the study. While this loss probably represents the aver- 

 age mortality from grazing over the Forest as a whole, yet it does 

 not adequately express the seriousness of the losses in certain impor- 

 tant parts of the Forest. Areas exist where more than 50 per cent 

 of the total number of young pines have been killed. Such areas 

 include many sections of the bunchgrass type south and west of 

 Lake Mary, the edges of parks, bedgrounds, driveways, the vicinity 

 of headquarter ranches and water holes, and range areas that have 

 been overgrazed for a long period. 



It is estimated from a comparison of the age and height of 265 

 trees that a yellow pine will ordinarily, if uninjured, reach a height 

 of 4.5 feet — above which it can withstand severe grazing injuries — 

 when 15 years old, but that if it is subject to repeated grazing injuries 

 it may require 35 years to reach this height. If it may be assumed 

 that under average conditions which prevail over the Forest it re- 

 quires 17 years for reproduction to reach a height of 4.5 feet, and 

 that, as shown in Table I, 0.9 per cent of all trees observed die an- 

 nually as a result of grazing injuries, it is safe to conclude that the 

 loss of trees during the period when they are subject to severe grazing 

 is approximately 15 per cent of the stand, or nearly as many as are 



