THE WESTERN" YELLOW PINE MISTLETOE. 23 



On an area of 456 acres on the Tusayan National Forest about 5 

 miles from the Fort VaUey Forest Experiment Station, 2,636 black 

 jacks, or 34.9 per cent of the total number on the plot, and 225 

 yellow pines, or 34.8 per cent of the total number, were infected with 

 mistletoe in 1914. In 1919, 2,335 black jacks, or 28.8 per cent of the 

 total number of trees 4 inches in diameter and over, were infected with 

 mistletoe. In many instances the infection was not sufficient to 

 render the tree unhealthy, but with the increase of infection many of 

 the infected trees will pass through the various infection classes and 

 eventually die. 



All of the trees which had died on the plots during the two 5-year 

 periods were carefully examined and the cause of death noted. On 

 the plot of 456 acres on the Tusayan National Forest 170 black jacks 

 died from various causes dm-ing the first 5-year period, or 2.2 per 

 cent of the total number of black jacks living on the plot in 1909, 

 while 21 yeUow pines died dm-ing the 5 years, which is 3.4 per cent 

 of the total number of yellow pines living on the area. During the 

 5-year period from 1914 to 1919, 127 black jacks died from mistle- 

 toe alone, or in conjunction with other agents such as insects, porcu- 

 pines, etc. 



On a plot of 135 acres located on the Coconino National Forest 

 about 1^ miles from the Fort VaUey Forest Experiment Station, 27 

 black jacks died from various causes during the first 5 years, which 

 is 1.1 per cent of the total number of black jacks living on the plot in 

 1 909; 26 yellow pines, or 1.8 per cent of the total number, died during 

 the same period. 



A digest of that part of the detailed records pertaining to mistletoe 

 as a cause of the death of western yellow pine during the 5-year 

 period from 1909 to 1914 is given in Table 17. The 456-acre plot on 

 the Tusayan National Forest is located on an area which has sus- 

 tained heavy losses from mistletoe, while the 135-acre plot on the 

 Coconino is located on an area with only occasional heavy infections. 

 A study of Table 17 indicates the mortality of v/estern yeUow pine on 

 these two areas and the extent to which mistletoe was a direct cause 

 or a contributing factor. A study of Table 17 also indicates that of 

 the 170 black jacks on the Tusayan plot which died during the 5- 

 year period 26.4 per cent were kiUed directly by mistletoe, 42.3 per 

 cent by mistletoe combined with other agents, and only 31.3 per cent 

 died from other causes; while only 4.8 per cent of the yellow pines 

 were killed by mistletoe combined with bark beetles. On the 135- 

 acre Coconino plot mistletoe infection alone resulted in the death 

 (Plate III, Fig. 2) of 7.5 per cent of the total nmnber of dead black- 

 jacks and 7.9 per cent of the total number of dead yeUow pines, while 

 mistletoe was a contributing factor toward the death of an additional 

 20.2 per cent of the yellow pines. During the 5 years 1.5 per cent 



