THE WESTERN YELLOW PINE MISTLETOE. 23 © 
On an area of 456 acres on the Tusayan National Forest about 5 
miles from the Fort Valley 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 during 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 yellow pines died during 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, ete. 
On a plot of 135 acres located on the Coconino National Forest 
about 14 miles from the Fort Valley 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 
1909; 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 western yellow 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 killed 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 number of dead black- 
jacks and 7.9 per cent of the total number of dead yellow 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 
