24 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE. 



(2) The most injured are the seedlings, 21 per cent of which are 

 seriously damaged. The damage gradually decreases with an increase 

 in the size of the trees. Trees above 4.5 feet in height are free from 

 severe injuries from browsing, but those between 3 feet and 6 feet 

 in height are likely to be rubbed severely. 



(3) The greatest amount of damage occurs during the latter half 

 of June and the first part of July, or 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 grow- 

 ing season and during the fall drying period. 



(4) Under normal conditions of grazing cattle and horses, and 

 incidentally burros, do an inconsiderable amount of damage to 

 reproduction. Sheep under the same conditions may be responsible 

 for severe injury to 11 per cent of the total stand. 



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

 trees severely. Cattle and horses may damage about 10 per cent of 

 all reproduction. Where sheep are grazed along with them, how- 

 ever, at least 35 per cent of the total stand may be severely damaged. 



Cattle and sheep are responsible for practically all of the grazing 

 damage to yellow pine on the Coconino forest. Ordinarily sheep 

 cause about seven and a half times as much damage as cattle. 



(5) The density of forage does not affect the amount of damage 

 that may be caused on a given area. 



(6) The suitability of the forage to the class of stock using a 

 range has an important influence upon the amount of damage to 

 timber reproduction. Because of the suitability of the pure bunch- 

 grass type to sheep grazing, the reproduction over approximately 

 one-third of the bunchgrass type on the Coconino Forest, or over 

 130,000 acres, is being seriously injured. 



(7) The amount of palatable feed available during the grazing 

 season, and especially during June and July, has an important bear- 

 ing upon the amount of damage that grazing will cause to reproduc- 

 tion. During a favorable year the damage may be 18 per cent less 

 than during a subnormal year. 



(8) 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. 



(9) Grazing is believed to have a largely neutral effect upon the 

 germination and early establishment of reproduction, but to have an 

 important effect in reducing the destruction of reproduction by fire. 



