14 —° BULLETIN 1112, U. S. DEPARTMENT OF AGRICULTURE. 
class. Jorty-year age classes were used instead of the usual 20-year | 
age classes, because they provided a greater number of trees as the Ht 
1g; 
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 
yellow pine trees, for a 25-year period, grouped by age classes and degree of mistletoe 
infection. 
| | 
Diam- Ac- | Ac- Ac- Ac- Ac- 
D eter cre- ere- cre- cre- } cre- 
a breast tion, | Diam-] tion, | Diam-| tion, | Diam-| tion, | Diam-} tion, 
8 - high.. |1990- | eter |1895-| eter |1900-| eter | 1905-| eter | 1910- 
Ageclass. is 1895, |breast| 1900, | breast} 1905, |breast| 1910, | breast| 1915, |Basis. 
of peri- | high, | peri- | high, | peri- | high, | peri- | high, | peri- 
tae odie | 1900. | odie | 1905. | odic | 1910. | odic | 1915. | odic 
tion.) 1899 | 1895 | an- an- an- an- an- 
nual nual nual nual nual 
Years Te, ae In. In. In. In. In. In. In. In. In. | Trees 
21 to'60es272 oO O38 Hid. Oot 0204 156 jy OF 12 Dor OA on ty | O28 550; 15:03:26 11 
x acd 6 .08 1.4 .16 2D aoe 3u0 . 20 4.4 18 6 
4 poe mi 4 . 06 .8 . 08 Lis -10 1.8 pl) yea . 06 a 
©. ERAS EE 40 . 06 .6 . 06 sah . 02 .9 . 04 len . 04 5 
61 t0100....) oO ape ears 4 510) 9.3 BO?) 10, 4 | rena ty Nig eeonte £3.60 . 30 12 
x 6:6" | 7:38 14 8.0 14 Boe ee 9.3 ke 9.9 a2 7 
Sea GOS Gr Bes etO kee 14) OBL RG ~LOt = OhOeeteS 9 
RK hee Os Sial ds De 14 8.2 .14 8.7 ao 9.2 .10 9.4 . 04 17 
101 to 140..-! o IG Aa a i Sir e144 16.5 a laa Ee fea 220: LS: '6 -22} 19.8 . 24 6 
eee. 14554) 25.4 De LD On) Gea) silat ee by Pa 516.) 18,3 .16 4 
EG: TE Se in ES SOSiis boy, 7 me CO oe pe -08 | 16.5 -08 | 16.9 - 08 6 = 
So | Pa 2a 6 .08 | 15.9 06°) 163 .08 | 16.7 .08 | 17.0 . 06 4 
201 to 240...) Oo 17.8 | 18.5 14] 19.3 -16} 20.1 PLO eeeek SQ0Giar aoe k . 20 5 
2 0 . 06 17.4 .08 7G . 06 17.9 . 04 18.2 . 06 5 
