Mar. 15, 1925 
Mortality of Trees Attacked by the Spruce Budworm 555 
ways be favored in preference to 
balsam. 
Mature softwood types were not 
studied in detail, though it is believed 
methods involving clear cutting with 
the object of securing more uniform 
second-growth stands in compartments 
of varying ages are more desirable. 
The history of these northern forests 
in the past has been largely the history 
of burns, the resulting second growth 
producing relatively more budworm- 
resistant forests, with lower percent¬ 
ages of balsam. There may be a lesson 
in this, suggesting periodic clear cut¬ 
ting, a case somewhat analogous to the 
better results secured by periodic re¬ 
newal of coppice forest by seedling 
trees. 
Diversified forests, both as to age 
classes and types, will aid in lowering 
the momentum of budworm outbreaks 
and result in less general and disastrous 
devastation. 
These recommendations are not to 
be considered as applicable to the Lau- 
rentian region. The entirely different 
silvicultural characteristics of the 
spruce of this region, the great diffi¬ 
culty of securing spruce reproduction, 
and the prolificness of balsam will de¬ 
mand different methods. 
SUMMARY 
The study herein reported indicates 
that there is a definite correlation be¬ 
tween the mortality occurring in spruce 
and fir stands (from spruce budworm 
defoliation) and the rate of growth of 
these stands prior to attack. The 
more rapid the rate of growth as ex¬ 
pressed in diameter increment the 
lower the resulting mortality under 
equal conditions of feeding. This rela¬ 
tion between the effects of budworm 
feeding and previous vigor is a more 
tangible quantity than any of the other 
factors heretofore considered and 
should serve as a practical basis for 
preventive measures through proper 
silvicultural practices which maintain 
rapid growth. 
A comparison of the rate of growth 
of trees surviving budworm attack 
shows that the diameter growth for 
the 10-year period following the first 
year of feeding is only about one-half 
that of the preceding 10 years. 
It was found that in hardwood types 
the immunity of softwoods was propor¬ 
tional to the protection of the overstory 
of hardwood foliage. The percentage 
of mortality among dominant soft¬ 
woods in mixed stands was as high as 
in pure softwood stands. 
