BULLETIN 580, XT. S. DEPARTMENT OF AGRICULTURE. 

 Table III. — Periodic damage. 



Period. 





fear. 



Total 



trees 



observed. 



Per cent 

 of trees 



Average 

 per cent 



Average 

 per cent 



No. of period. 



Begin- 

 ning. 



1 



v-r^v,,-, Number 

 Ending. 0fweek5 . 



"5 



found 

 damaged 

 at each 

 exami- 

 nation. 



of trees 

 damaged 



each 

 grazing 

 season. 



of trees 

 damaged 

 per -week 



each 

 grazing 

 season. . 



First 



Apr. 15 

 May 21 

 July 9 

 Sent. 13 



May 20 

 July 8 

 Sept. 12 

 Nov. 6 



5 

 7 



9 



f 1912 . 



1913. 



(1912. 

 11913. 



(1912. 

 11913. 



Average. 

 Average. 

 Average. 

 Average. 



8,945 

 8,945 



0.3 

 .4 



1 0.35 



!„, 



0.07 



Second 



8,945 



S. 945 

 8,945 



.35 



14.0 

 22.0 



2.5 



Third 



8.945 



8.945 

 8.945 



18.0 • 



35.0 

 36.0 



1.9 





[1912. 

 8 1913 - 



S,94o 



35.5 





Fourth 



8,945 

 8.945 



46.0 

 40.0 



.9 







8,945 



43.0 





The observations indicate that the greatest amount of damage 

 occurs during the latter half of June and early in July, or during 

 the severest portion of the early summer dry period, and that the 

 least damage occurs during the first few weeks of the grazing period. 

 or before June 1. A considerable amount of damage occurs during 

 the main growing season and a smaller amount during the fall drying 

 period. 



The fact that a relatively small amount of damage occurred during 

 1914. which was unusually favorable for the growth of forage, gave 

 support to the theory that the severity of damage varies inversely as* 

 the amount of succulent feed available. The record of periodic 

 damage, however, indicates that there is an important factor besides* 

 the amount of available succulent forage which determines the 

 severity of damage. This is believed to be the condition of the cur- 

 rent year's growth of pine shoots. All observations substantiate the 

 belief that, except in unusual cases, stock will not injure coniferous 

 shoots of a previous year's growth. It has been noted particularly 

 that during the early summer practically no damage occurs until new 

 shoots appear, and that damage in any year is confined largely' to 

 that year's growth. Yellow-pine vegetative buds start active growth 

 on the Coconino Forest about May 15, and by June 20 have formed 

 succulent shoots with well-developed needles. From that time until 

 about the middle of August the shoots are tender and more palatable 

 than at other periods. Thus the season of best forage growth is also 

 the period when yellow-pine shoots are most palatable. This and 

 the probability that during the severe spring dry period stock develop 

 a taste for the pine shoots which continues during the early portion 

 ol the summer growing period may explain the rather severe dam- 



