Mar. 15, 1925 
Mortality of Trees Attacked by the Spruce Budworm 551 
Considering mortality in the hard¬ 
wood plots, Tables XII and XIII, 
where defoliation was severe on the 
free trees and relatively lighter in the 
overtopped trees, it is shown that 
balsam mortality of free trees is similar 
to that in softwoods (as illustrated in 
fig. 3); among the overtopped trees it 
falls quite regularly from the smaller 
diameters to the higher. Red spruce 
mortality among the free trees is 
similar to that of softwood stands (as 
illustrated in fig. 3); among the 
overtopped trees it falls quite regu¬ 
larly from the smaller diameters to 
the higher. White spruce mortality 
among the free trees falls rapidly as 
diameter increases and is lower than 
white spruce in the softwoods; among 
the overtopped trees the mortal¬ 
ity falls similarly to that of red 
spruce, although it is higher in 
all diameters. 
It might be assumed that the 
correlation drawn between rate 
of growth and mortality is not 
conclusive from the fact that the 
position of the tree in relation 
to the' crown influences the 
amount of defoliation (inter¬ 
mediate and suppressed trees re¬ 
ceive relatively more defoliation 
in severe epidemics), and degree 
of defoliation is no doubt the 
most important factor causing 
death. In other words, may not 
the higher mortality of slower- 
growing trees be a result of their 
position? 
This is clearly not the case with 
balsam, which is subject to heavy 
defoliation, since greater mortal¬ 
ity occurs as diameter increases, 
and there was found to be no cor¬ 
relation between rate of growth 
and mortality for such heavily 
defoliated balsam. 
With red spruce receiving severe 
defoliation both in pure softwoods and 
free trees in hardwood stands the great¬ 
est mortality occurs between the diame¬ 
ter classes 6 and 8 inches, which trees 
in these 60-year stands would be 
largely either dominants or codomi¬ 
nants. 
In the case of white spruce receiving 
heavy defoliation, greatest mortality 
does occur in the lower-diameter classes 
3, 4, and 5 inches, and here it is impos¬ 
sible to decide how much of the mor¬ 
tality is due to position, suppression, or 
budworm defoliation. In hardwood 
stands (Table XVII) greater total mor¬ 
tality occurs in the overtopped trees, 
which receive less defoliation, than in 
the free trees. On the other hand, with 
lighter feeding, mortality in all species 
is greater in the lower-diameter classes, 
which, of course, on the whole are 
slower-growing trees, but here again in 
balsam, which receives more defolia¬ 
tion, the mortality persists well up into 
high-diameter classes (both in softwood 
stands and overtopped trees in mixed 
hardwood stands) where many of the 
trees in softwood stands would be domi¬ 
nants and codominants. 
It is not intended to argue that posi¬ 
tion does not have a certain effect on 
mortality, yet it seems impossible this 
long after the budworm feeding to de¬ 
termine just what weight can be at¬ 
tributed to it. 8 Referring to Table I, 
it will be seen that there is little differ¬ 
ence in the average diameter of trees 
dying over a three-year period, while 
rate of growth and percentage of defo¬ 
liation show regularly increasing or de¬ 
creasing values in respect to time of 
death. 
COMPARISON OF RADIAL INCRE¬ 
MENT OF SOFTWOODS BEFORE 
AND AFTER BUDWORM ATTACK 
These series of measurements (Table 
XVIII and fig. 5) were taken to com¬ 
pare the rate of growth of partially de¬ 
foliated trees before and after the bud¬ 
worm attack. The trees were se¬ 
lected promiscuously over the areas on 
which the foregoing plots were taken. 
Only dominant or codominant trees 
Fig. 4.—Mortality of spruce and fir in various forest types 
resulting from light defoliation in hardwood mixtures by the 
spruce budworm, shown by diameter classes. The balsam 
(hard wood), red spruce, and white spruce are overtopped 
8 The degree of feeding on individual trees could not be determined at the time of this study. 
