14 



BULLETIN 1112, U. S. DEPARTMENT OF AGRICULTURE. 



class. Forty-year age classes were used instead of the usual 20-year 

 age classes, because they provided a greater number of trees as the 

 basis for each age and infection class. 



The harmonized volume-age curves for the 21 to 60 and the 61 to 

 100 year age classes are shown in Figure 3, which indicates that the 

 mistletoe infection was sufficiently severe to retard the rate of growth 

 of the more heavily infected trees of these two age classes by approx- 

 imately 20 years. Figure 4 shows a similar retardation of the incre- 

 ment for the 101 to 140 and the 201 to 240 year age classes, except 

 that the rate of growth of the more heavily infected trees of these age 

 classes has been on the decline for the past 70 to 80 years. The 

 curves in both figures show conclusively that the current increment is 

 directly dependent upon the degree of mistletoe infection. Gener- 

 ally speaking, the degree of mistletoe infection increases with the 

 length of time which a tree has been infected. 



A further comparison of the average diameter growth or accretion 

 of the felled western yellow pine trees for the 25-year period from 

 1890 to 1915, grouped by 40-year age classes and degree of mistletoe 

 infection, is shown in Table 8. A similar comparison of the average 

 height growth or accretion of the same trees is given in Table 9. 

 Table 10 shows a comparison of the average volume growth or incre- 

 ment of the same trees for the same period, similarly grouped by age 

 and infection classes. The 21 to 60, 61 to 100, and the 101 to 140 year 

 age classes in Tables 8, 9, and 10 are composed entirely of black jacks, 

 while yellow pines constitute the 201 to 240 year age class. 



Table 8. — Comparison of the average diameter growth or accretion of 102 felled western 

 yelloiu -pine trees, for a 25-year period, grouped by age classes and degree of mistletoe 

 infection. 







Diam- 



Ac- 





Ac- 





Ac- 





Ac- 





Ac- 







De- 



eter 



cre- 





cre- 





cre- 





cre- 





cre- 







breast 



tion, 



Diam- 



tion, 



Diam- 



tion, 



Diam- 



tion, 



Diam- 



tion, 







gree 



high. 



1890- 



eter 



1S95- 



eter 



1900- 



eter 



1905- 



eter 



1910- 





Age class. 



of 

 in- 

 fec- 

 tion. 





1895, 

 peri- 



breast 

 high, 



1900, 

 peri- 



breast 

 high. 



1905, 

 peri- 



breast 

 high, 



1910, 

 peri- 



breast 

 high. 



1915, 

 peri- 



Basis. 

















odic 



1900. 



odic 



1905. 



odic 



1910. 



odic 



1915. 



odic 







1890 



1895 



an- 





an- 





an- 





an- 





an- 













nual. 





nual. 





nual. 





nual. 





nual. 





Years. 





In. 



In. 



In. 



I7l. 



In. 



In. 



In. 



In. 



In. 



In. 



In. 



Trees. 



21 to 60 







0.8 



1.0 



0.04 



1.6 



0.12 



2.3 



0.14 



3.7 



0.28 



5.0 



0.26 



11 





X 



.2 



.6 





08 



1.4 



.16 



2.5 



.22 



3.5 



.20 



4.4 



.18 



6 





XX 



.1 



.4 





06 



.8 



.08 



1.3 



.10 



1.8 



.10 



2.1 



.06 



7 





XXX 





.3 





06 



.6 



.06 



• .7 



.02 



.9 



.04 



1.1 



.04 



5 



61 to 100.... 







"7.' 2' 



8.2 





20 



9.3 



.22 



10.4 



.22 



11.5 



.22 



13.0 



.30 



12 





X 



6.6 



7.3 





14 



8.0 



.14 



8.7 



.14 



9.3 



.12 



9.9 



.12 



7 





XX 



6.0 



6.8 





16 



7.5 



.14 



8.1 



.12 



8.6 



.10 



9.0 



.08 



9 





XXX 



6.8 



7.5 





14 



8.2 



.14 



8.7 



.10 



9.2 



.10 



9.4 



.04 



17 



101 to 140... 







15.0 



15.7 





14 



16.5 



.16' 



17.5 



.20 



18.6 



.22 



19.8 



.24 



6 





X 



14.5 



15.1 





12 



15.9 



.16 



16.7 



.16 



17.5 



.16 



18.3 



.16 



4 





XX 



14.8 



15.2 





08 



15.7 



.10 



16.1 



.08 



16.6 



.08 



16.9 



.08 



6 





XXX 



15.2 



15.6 





08 



15.9 



.06 



16.3 



.08 



16.7 



.08 



17.0 



.06 



4 



201 to 240... 







17.8 



18.5 





14 



19.3 



.16 



20.1 



.16 



21.1 



.20 



22.1 



.20 



5 





XXX 



10.7 



17.0 





06 



17.4 



.08 



17.7 



.^6 



17.9 



.04 



18.2 



.06 



5 



