550 
Journal of Agricultural Research 
Vol. XXX, No. 6 
decreasing in the smaller and larger 
trees; in white spruce highest mortality 
occurs in the smaller-diameter classes, 
decreasing in the higher diameters. 
Fig. 3.—Mortality of spruce and fir in various forest types 
resulting from severe defoliation by the spruce budworm, 
shown by diameter classes. The white spruce (hard¬ 
wood) are free 
becoming decadent, and suggests that 
“the conifers, after years of competition 
in hardwood mixtures, are even less 
resistant than those in softwood stands. 
Some indication of the relative 
ability of these trees to withstand 
severe competition is obtained 
from the tables summarizing the 
hardwood plots (Tables XII, XIII, 
XIV, and XV) and that of the 
mortality by diameter classes 
(Table XVII), suggesting that 
white spruce is least resistant as 
indicated by the higher mortality 
of the overtopped trees of the 
birch-poplar type (Tables XII and 
XIII), and the higher percentage 
of mortality in the 3, 4, and 5 inch 
diameter classes of softwood types. 
The same tables indicate that bal¬ 
sam can withstand more competi¬ 
tion than white spruce and that 
red spruce is the most resistant 
species. 
MORTALITY BY DIAMETER 
CLASSES WITH SEVERE AND 
LIGHT DEFOLIATION 
The following table of the tree 
mortality (Table XVII) of three 
series of plots tabulated by diameter 
classes is given to show the relative effects 
of different degrees of caterpillar feeding 
on the various softwoods concerned and 
how such feeding affects mortality in 
the larger and smaller tree classes. 
Considering the same combination 
but with lighter feeding (fig. 4) as 
occurred at Metis, where the red and 
white spruce are very little affected 
(in fact, it might be questioned if 
Table XVI.— Percentages showing softwood composition before budworm attack 
and total mortality for each series of plots 
Balsam 
[ 
Red spruce 
White spruce 
Mortality 
Composi¬ 
tion 
Mortality 
Composi¬ 
tion 
Mortality 
Composi¬ 
tion 
Softwoods from Tables IV and V_ 
Softwoods from Tables VI and VII_ 
Softwoods from Tabled VIII and IX_ 
Softwoods from Tables X and XI_ 
Hardwoods from Tables XII and XIII_ 
Free trees (alone)___ 
Overtopped trees (alone) _ _ 
Hardwoods from Tables XIV and XV_ 
Free trees (alone).. _ 
! 
Per cent 
5.2 
9. 5 
27.4 
79.1 
34.2 
60.8 
39. 2 
46. 7 
61. 2 
38.8 
Per cent 
66.2 
59. 5 
60.2 
39. 1 
53.0 
78. 5 
38.8 
27. 2 
58.8 
9.9 
Per cent 
94.8 
72. 1 
33.3 
5.3 
50. 3 
61.3 
38.6 
53.3 
64.3 
35. 7 
Per cent 
29.8 
22 . 1 
27.9 
5.5 
13.4 
23.6 
7. 6 
20.5 
39. 6 
5.4 
Per cent 
18.4 
39.2 
15.6 
15.4 
68.0 
32.0 
Per cent 
40.6 
37.3 
11.6 
20.2 
18.7 
21.8 
Overtopped trees (alone) ... 
' '1 
Considering the mortality of the 
three species of trees concerned by 
diameter classes and under conditions 
of heavy defoliation (fig. 3) (such as is 
represented by softwood stands of 
Tables VIII and IX) it is shown that 
in balsam mortality is relatively high 
in all classes, but increases with diame¬ 
ter; in red spruce highest mortality 
occurs in the middle-diameter classes, 
mortality in these two species can be 
attributed to other than natural thin¬ 
ning), we find that in balsam greatest 
mortality occurs in smaller-diameter 
classes, decreasing with larger diame¬ 
ters; in red spruce all mortality occurs 
in low-diameter classes below 6 inches; 
in white spruce all mortality occurs in 
low-diameter classes below 6 inches. 
