THE WESTERN YELLOW PINE MISTLETOE. 



Table 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. 



Degree of infection. 



Total volume. 



Increment, 1910-1915. 



Basis. 



1910 



1915 



Periodic. 



Periodic annual. 







Cubicfeet. 



1, 151. 



1,206.0 



706.0 



801.0 



Cubicfeet. 



1, 226. 



1,250.0 



725.0 



809.0 



Cubicfeet. 



75.0 



44.0 



19.0 



8.0 



Cubicfeet. 

 15.0 

 8.8 

 3.8 

 1.6 



Per cent. 



1.30 



.73 



.54 



.20 



Trees. 



9 



X 



8 



XX 



7 



XXX 



19 







1 Five trees of this class died during the 5-year period arid were not inelu(ied in the computation. 



Table 3 shows the total volume growth or increment of the stand- 

 mg 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 appUed 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 shght 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 groimd, 



3 This is known as the Smalian method. See Graves, Henry S., Forest Mensuration, pp. 91-93, New 

 York, 1907. 



