THE WESTERN YELLOW PINE MISTLETOE. c~ 
- Taste 4.—Comparison of the total volume growth or increment of 33 standing yellow 
pines, for a 5-year period, grouped according to degree of mistletoe infection. 
Increment, 1910-1915. 
Degree of infection. 
Cubic feet. | Cubic feet. | Cubic feet. | Cubicfeet. | Per cent. Trees 
a ee | 1,151.0 | — 1,226.0 | 75.0 15.0 1.30 9 
impale petite cieadieipe igi 1, 206. 0 1, 250. 0 | 44,0 8.8 | re 8 
Th ee 2 ee oe 706. 0 725.0 | 19.0 3.8 | 54 7 
ace Sie pec ie ils Mai ae 801.0 mee 8.0 1.6 | 20 19 
1 Five trees of this class died during the 5-year period and were not included in the computation. 
Table 3 shows the total volume growth or increment of the stand- 
g ing black jacks for the same 5-year period, grouped by infection 
classes. The total volumes were computed by applying a volume table 
based on diameter and total height to the dimensions of each tree as 
measured in 1910 and 1915. It was found from taper measurements 
that volume tables could safely be applied to the individual trees. 
The volumes of all trees were totaled by infection classes. The differ- 
_ ence between the total volumes at each time of measurement repre- 
sents the periodic increment, and the average volume growth per 
year during the period considered is the periodic annual increment. 
Table 4 shows the increment of the standing yellow pines for the 
same 5-year period. Both forms of western yellow pine exhibit a 
consistent decrease in the increment of those trees which are infected 
with mistletoe varying directly with the degree of infection. 
Bole measurements were made at 16-foot intervals to insure greater 
accuracy in the study of the effect of mistletoe on the growth of the 
merchantable contents of the bole of the tree. Table 5 gives a compar- 
ison of the diameter growth of the bole of 33 trees at 4.5, 17, and 33 
feet above the ground. The comparative increments of the same 
trees are shown in Table 6. The apparent discrepancy between the 
_ rate of growth of the uninfected and lightly infected classes, as was 
noted above, is apparently due either to the varying proportions of _ 
the trees among the different crown classes or it may be possible that 
the infection at first results in a slight stimulation of the tree. In 
computing the volume, each section below the highest point of meas- 
urement was cubed as a cylinder by averaging the basal areas of the 
ends and multiplying by the length of the section;? that portion above 
was considered as the top of the tree and its volume was computed as 
that of a cone. 
The growth of the standing trees was further checked by complete 
stem analysis of 102 felled trees. Sections were examined as near 
to the surface of the ground as possible, at 4.5 feet above the ground, 
3 This is known as the Smalian method. See Graves, Henry S., Forest Mensuration, pp. 91-93, New 
York, 1907. 
