REGULATION OF GRAZING 373 



2. Season of Injury: "The greatest amount of damage occurs during the 

 latter half of June and the first part of July when the effects of the spring 

 dry period are most pronounced. The least damage occurs during the first 

 few weeks of the growing period, or before June 15. A very considerable 

 amount of damage is done during the main growing season and during the 

 fall drying period." 



J. Amount of Damage and Intensity of Grazing: Under normal conditions 

 of grazing, sheep may be responsible for severe injury to 11 per cent of the 

 reproduction under 5^4 feet. Cattle and horses under normal grazing do an in- 

 considerable amount of damage. Hill defines normal grazitig as grazing where 

 the rmmber of stock is well adapted to the character and amount of forage. 



On overgrazed areas, however, all classes of stock are apt to damage small 

 trees severely. Cattle and horses may injure about 10 per cent of all repro- 

 duction. Where sheep are grazed along with cattle and horses at least 35 per 

 cent of the to4al reproduction may be severely damaged. Ordinarily sheep cause 

 about 71/2 times as much damage as cattle. 



"The manner in which stock is handled has much to do with the severity of 

 grazing damage. Cattle are likely to injure 22 per cent of the trees between 

 3 feet and 6 feet in height that grow on areas where they are accustomed to 

 congregate. Sheep severely injure reproduction along driveways and on bed 

 grounds." 



4. Amount of Damage and Character of Forage: The suitability or lack of 

 suitability of forage on the range to the class of stock has an important influ- 

 ence on the amount of damage to timber reproduction. The general conclu- 

 sion that but 11 per cent of the reproduction may be injured by normal sheep 

 grazing is believed to apply to grama grass range. On bunchgrass range, how- 

 ever, the damage may be more serious, even though the range is not grazed 

 qlosely. A special study of sheep grazing on bunchgrass ranges showed a total 

 of 32 per cent of the reproduction subject to injury was severely browsed dur- 

 ing 1912 and 1913. A continuation of the conditions then existing would re- 

 sult in severe injury to at least 32 per cent. On a number of plots practically 

 every tree had been killed by grazing. The bunchgrass range under observa- 

 tion was in the north half of the Forest where the bunchgrasses occur in purer 

 stand than is ordinarily the case. Hill concluded, however, that where bunch- 

 grass forms the main part of their feed sheep grazing may result in severe 

 damage to yellow pine reproduction. 



Consistent with the conclusions regarding variation in damage to reproduc- 

 tion, due to lack of suitable feed, Hill found that damage during favorable 

 years for forage production was much less than during years of average or 

 less than average production. 



Hill's data are lacking as to injury to seedlings immediately follow- 

 ing germination. This omission in the investigations was due to the 

 fact that in unfavorable years of the Southwest practically all seedlings 

 which germinate die without injury from grazing, and at best a large 

 percentage die. To determine the part grazing plays during this 

 early age would be difficult as a part of the study undertaken. 



