EFFECT OF GRAZING ON WESTERN YELLOW PINE. 



11 



AMOUNT OF FORAGE BY SEASONS. 



The fact that a greater amount of damage occurs during the dry 

 period of early summer, when ordinary forage is scarce, than during 

 other periods of the grazing season suggests the probability that dur- 

 ing a season when feed is unusually abundant the amount of damage 

 will be relatively small. This supposition is confirmed by a com- 

 parison of the damage done in 1914 with that done in 1913. 



Ordinarily not enough precipitation occurs during May and June 

 10 support the vegetative growth, and as a result not enough forage is 

 produced to meet the needs of stock. This was the cae in 1913 ; but 

 in 1914 the dry period was broken in June by sufficient rainfall to 

 revive the forage, and this was followed by abundant rainfall in July 

 and August. Since the three months from June to August form the 

 main growing period, 1914 was an unusually favorable year for 

 the production of forage, and 1913 an unusually poor one. (See 

 Table IV.) 



TABLE IV. Precipitation during the growing periods of 1913 and 1914* 



i The monthly rainfall is an average for the entire yellow-pine type, based upon the records at Fort 

 Valley, Flagstaff, and Walnut Canyon. 



TABLE V. Comparison of the Kerioufs damage caused on grazing during 1913 



and 1914. 



Trees seriously 

 damaged. 



Table IV indicates that vegetation could not have made any con- 

 siderable growth in 1913 before July, and the record of periodic 

 damages shows that more than one-half of the total annual damage 

 for that year occurred during this dry period. Xo record of periodic 

 damage was kept in 1914, but a summary for the year (see Table V) 

 reveals 13 per cent of the entire number of trees seriously damaged, 

 as compared with 15.8 per cent for 1913. The lower per cent of 

 damage for 1914 is believed to be due chiefly to the greater abundance 

 of feed during that year, particularly during June and early in July. 



