KAXGE MANAGEMENT ON THE NATIONAL FORESTS. 67 



guide in making necessary adjustments Trliere otlier conifer species 

 are involved. 



Inteixsity of grazing. — Tiie injury to conifer reproduction from 

 grazing by any class of stock varies directly with the intensity of 

 grazing. Hill ^ found in Arizona and New Mexico that " on over- 

 grazed areas all classes of stock are apt to damage small trees (west- 

 ern yellow pine) severely. Cattle and horses may damage about 10 

 per cent of all reproduction. T^liere sheep are grazed along with 

 them, however, at least 35 per cent of the total stand may be severely 

 damaged. Ordinarily sheep cause about seven and one-half times as 

 much damage as cattle." Under normal conditions of gTazing, Hill 

 f omid that " cattle and horses do an inconsiderable amount of damagei 

 to western yellow-pine reproduction, but that sheep may be respon- 

 sible for severe injury to 11 per cent of the total stand of reproduc- 

 tion under about 4 feet in height." 



Sparhawk^ found in., central Idaho that from 20 to 30 per cent 

 of seedlings less than 1 year old were killed by sheep grazing and 

 trampling on moderately grazed areas and 6.5 per cent on lightly 

 grazed plots. On moderately grazed areas only about 1 per cent of 

 the yellow-pine reproduction over 3 years of age was killed. Mod- 

 erate grazing means removal of the greater part of the forage readily 

 eaten by sheep. 



Character of fm^age. — If there is an abundance of forage suitable 

 for stock there will be little damage to tree reproduction by browsing. 

 On the other hand, if there is little forage suited to the class of stock, 

 especially sheep, the tree growth within reach will be browsed. This 

 is why moderate grazing by sheep is defined as removal of the greater 

 part of the forage readily eaten by sheep. Grazing until the less 

 palatable forage is eaten will result in marked increase of damage to 

 3'oung tree growth, both from browsing and trampling. 



Hill found that on range where the greater part of the forage is 

 bunch grasses, sheep injured 32' per cent of the western yellow-pine 

 reproduction under about 4 feet in height. The same intensity of 

 grazing on range better suited to sheep resulted in severe injury to 

 only about 10 per cent of the reproduction. The bunch grasses were 

 not overgTazed, but they are not suitable for the main forage for 

 sheep. Even light grazing would result in considerable damage to 

 the young trees. Cattle on the same range would do little damage if 

 overgTazing were avoided. 



Tirne of grazing. — Both Hill and Sparhawk found that injury to 

 tree reproduction is least when the range is grazed during the time 



1 Hill, Robert R. Effects of Grazing upon Western Tellovi' Pine Reproduction in the 

 National Forests of Arizona and New Mexico. U. S. Department of Agriculture, Bui. 580, 

 1017. 



^ Simrhawk, W. N. Effect of Grazing upon Western Tellow Pine Reproduction iu 

 Central Idaho. U. S. Dept of Agriculture, Bui. 738, 1918. 



