356 FOREST INDICATORS. 



Hill (1917: 23) has reached the following conclusions with reference to the 

 damage done to seedlings in the yellow-pine forests of northern Arizona: 



"Of 8,945 trees of a size subject to grazing, observed over a period of three 

 years, 1,493 or 16.7 per cent were severely damaged each year and 1,222 

 or 16.1 per cent were moderately damaged. 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 damage by browsing. 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. Under normal con- 

 ditions of grazing, cattle and horses 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, however, at least 35 per cent of the total stand may be 

 severely damaged. The amount of palatable feed available during the graz- 

 ing season, and especially during June and July, has an important bearing on 

 the amount of damage that grazing will cause to reproduction" (plate 89). 



Sparhawk (1918) has shown that the damage to seedlings more than a 

 year old is negligible in the yellow-pine forests of central Idaho, while the 

 mortality of seedlings less than a year old averages 20 per cent. He states 

 that, on the whole — 



"More than three times as many seedlings were killed by other causes as 

 were killed by sheep grazing, and five times as many were injured. As a 

 general rule, the range should be grazed just enough to remove the greater 

 part of the palatable forage. Extensive browsing of the least palatable species 

 or of conifer reproduction is the best evidence that the area is being grazed 

 too closely not only for the good of the range, but also for the best interest of 

 the stock. Steep slopes with loose soil, particularly where the seedlings are 

 less than a foot and a half high, and reproducing burns, clear-cut areas, or 

 plantations with seedlings up to 5 or 10 years old, depending on the site, 

 should be grazed rather lightly, especially in the first part of the season or 

 during a wet period. In many instances it will be desirable to eliminate 

 grazing entirely from plantations or other areas of seedlings less than three 

 years old. During a dry season spots where danger of fire is greatest may be 

 grazed as closely as possible." 



Sampson (1919: 25) has summarized the results of his study of the effect 

 of grazing upon aspen reproduction as follows: 



"The leafage, young twigs, and branches of the reproduction are browsed 

 with varying degrees of relish by both cattle and sheep. Over 90 per cent of 

 the damage inflicted by stock is chargeable to browsing, the injury due to 

 trampling, rubbing, and similar causes being negligible. Sheep are responsible 

 for severe damage to the reproduction, both as it occurs in standing timber and 

 on clear cuttings, regardless of the variety and supply of choice forage. Cat- 

 tle cause some damage, but the extent of injury is usually slight, except where 

 the lands are overgrazed or where the animals are inclined to congregate for 

 more or less lengthy periods. The injury and mortality chargeable to the 

 presence of live stock is roughly proportional to the closeness with which the 

 lands are grazed. Observations covering a 50-year period in standing timber 

 on sheep range showed that 27.2 per cent of the reproduction was either in- 



