Mar. 15, 1925 
Mortality of Trees Attacked by the Spruce Budworm 543 
them to migrate in search of more suc¬ 
culent food. It is possible that slower- 
growing white-spruce trees putting out 
a less quantity of new growth are en¬ 
tirely defoliated of the current year’s 
needles before they harden. Red 
spruce, the buds of which open 10 to 
12 days later than balsam and white 
spruce (shortly before the larvae begin 
migrating), furnishes a second supply 
of succulent needles at a time when the 
larvae are most voracious; consequently 
much of it is consumed. 
The density of the stand affects the 
degree of defoliation in that migrating 
larvae have a better chance of falling 
on other food before striking the 
ground, from which they can not regain 
the trees. As a result of this migrating 
habit of the larvae no trees, even 
balsam, standing in the open are 
defoliated of more than their new 
growth. 
Higher percentages of balsam and 
white spruce encourage to a certain 
extent heavier defoliation on account of 
the greater supply of desirable food 
(early new growth), which enables the 
larvae to develop rapidly in their early 
stages. 
Balsam is always more severely 
defoliated than white or red spruce, 
since the old needles are also con¬ 
sumed; consequently, the feeding is 
less uniform and offers an explanation 
for lack of correlation between mor¬ 
tality and rate of growth under condi¬ 
tions of severe feeding. White and 
red spruce are defoliated only of the 
new growth, white usually to a lesser 
degree than red, and both more uni¬ 
formly than balsam. The amount of 
defoliation on the balsam sample plots 
.at Lake Opasatika, Quebec, from 1918 
to 1921 is shown in Table II. 
Dominant trees, especially those 
highest in the stand, are less severely 
defoliated than those beneath, owing to 
the migrating habits of the larvae. 
Table III illustrates this feature on the 
balsam sample plots at Lake Opasa¬ 
tika. The figures apply only to old 
foliage, since all the new growth was 
consumed each year. 
Thus the under story, which at the 
same time is composed of slower- 
growing trees, receives more defoliation. 
This does not apply to light outbreaks 
when, with abundance of food, the 
larvae do not migrate. 
SECOND-GROWTH SOFTWOOD AND 
BUDWORM MORTALITY 
Two widely separated areas were 
considered in these studies, centering 
about Bathurst, New Brunswick, and 
Metis Lake, Quebec. 
The Bathurst plots were located 
about 15 to 20 miles south of Bathurst, 
on the Tabusintac drainage. The soil 
is of a light sandy character, formed 
from the millstone grit of the middle 
Carboniferous. It is fairly thin and 
subject to excessive drying out, except 
on the hardwood ridges, where it is 
much deeper and of a loamy character. 
It fairly well characterizes the Mira- 
michi watershed, noted for its spruce 
forests. 
The other series of plots were taken 
on the south shore of the St. Lawrence 
River near the height of land between 
the Metis and Patapedia Rivers, on a 
seigniory of Price Brothers at Metis 
Lake, Quebec. It is essentially a soft¬ 
wood region, only scattered yellow and 
white birch occurring, except on the 
tops of the higher hills. Some 40 
years ago the area was very heavily 
cut over, so that the present stand 
averages about 75 years of age. A 
few older trees occurred on many plots. 
An attempt was made to secure the 
plots in more uniform younger growth 
and at the same time to select plots 
which showed higher mortality. Con¬ 
sequently, these figures are not quite 
typical of the area. 
In the vicinity of Bathurst 40 plots 
were tallied in practically pure soft¬ 
wood stands. An attempt was made 
to group these by series conforming to 
site qualities, types, and age classes. 
Tabulation of 24 plots is given occur¬ 
ring on a 65-year burn representing three 
sites of the spruce flat type. The 
remaining plots were more scattered in 
Table II.— Percentage of trees in arbitrary defoliation classes 
Degree of defoliation___ 
100 ! 
90 
75 
50 
25 
10 
Percentage of trees in class_ __ _ __ 
5.6 
10.6 
16.9 
33.2 
23.8 
9.9 
Table III.— Percentage of defoliation by diameter classes 
Diameter breasthigh, inches _ 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
Number of trees_ 
4 
47 
65 
31 
57 
54 
44 
30 
19 
11 
11 
Average defoliation, per cent. .. 
54 
77 
66 
64 
51 
46 
42 
29 
28 
28 
14 
