554 
Journal oj Agricultural Research 
Vol. XXX, No. 6 
Our knowledge of how budworm 
outbreaks originate and the factors 
necessary for their phenomenal in¬ 
crease and spread is so meager that any 
recommendations for the prevention of 
future outbreaks are only speculative. 
When outbreaks do occur, we can hope 
for little relief from direct control 
measures, though prompt salvage of the 
defoliated material will greatly reduce 
the total losses. 
With such limited possibilities of pre¬ 
vention or control before us, the only 
alternative is to keep the future forests 
in a condition least susceptible to the 
effects of defoliation. It is believed 
that the present study indicates that 
this can be accomplished by maintain¬ 
ing thrifty and vigorous stands. 
This result can only be secured in 
natural stands by judicious cuttings to 
reduce the density and promote more 
rapid increment in the individual trees. 
As an example, in second-growth 
stands, such as those under considera¬ 
tion, varying from 20 to 50 cords per 
acre at 40 to 50 years of age, it would 
certainly be practical to make a pulp- 
wood cutting when competition be¬ 
comes so severe as to induce high mor¬ 
tality from defoliation. Such an oper¬ 
ation should remove from 5 to 10 cords 
per acre, so as to make it profitable, 
and it should be conducted with the 
idea of maintaining trees of better qual¬ 
ity. 
The selection of the trees for thin¬ 
ning should be governed by the follow¬ 
ing considerations: 
Remove all the balsam possible to 
the smallest possible diameter limit, 
since it is most susceptible to bud- 
worm defoliation, promotes heavy feed¬ 
ing, and may be an important factor in 
originating outbreaks. Any balsam 
that is left should be single, thrifty, 
dominant trees. Groups of balsam 
should never be left. 
Remove all inferior red and white 
spruce and those that will not gain 
dominance by the time the next logging 
operation is contemplated. 
Between doubtful red spruce and 
white spruce favor red spruce, since it 
better withstands adverse conditions 
and is a more persistent grower. The 
presence of red spruce is least effect¬ 
ive in promoting severe budworm de¬ 
foliation. 
These thinnings should induce re¬ 
production and, judging by the effect 
of bud-worm thinnings, this regenera¬ 
tion may be largely balsam. How¬ 
ever, by removing practically all of the 
balsam and by breaking the soil litter 
through logging, possibly a high per¬ 
centage of spruce can be secured. 
If the stands are being managed for 
pulp wood, 10 to 20 years later, after 
reproduction is established, clear cut- 
ting should be adopted. In this case 
the new crop could again be mixed 
with balsam. 
If saw material is desired later, pulp- 
wood thinnings should be made to 
reduce density and promote more 
rapid growth, following the same selec¬ 
tion as before but favoring red spruce 
still more because of its quality of 
persistent growth. 
Balsam and white spruce should 
only be grown on the better sites. On 
these balsam is sufficiently immune to 
budworm feeding up to 40 years to 
leave a well-stocked stand, though 
several years' increment will be lost 
and the rotation lengthened. 
In the spruce swamp type, where 
reproduction is very good and balsam 
practically negligible, some form of 
selection system is advocated which 
would aim to remove mature and less 
thrifty trees, giving room for younger 
trees which grow more rapidly. 
Further study is needed in this type 
to determine the causes of periodic 
cycles of rapid growth in older stands 
and the conditions favoring rapid 
growth observed in younger stands 
following fires. 
Any recommendations in hardwood 
mixtures are dependent on the possi¬ 
bilities of utilization of the hardwoods. 
Since hardwoods are only a protection 
to the softwoods while the latter are 
overtopped, and since once the soft¬ 
woods gain dominance the mortality 
of balsam from the budworm is as high 
or higher than in pure softwoods, even 
greater care will be necessary to handle 
these mixtures successfully. 
In the birch and poplar type, which 
is a transitional stage in the formation 
of the spruce flat type, the hardwoods; 
should be regarded as purely a shelter, 
and the earlier the conifers are liber¬ 
ated the better. 
In the yellow birch and northern 
hardwood types, where the softwoods 
grow very rapidly and where practical 
conversion to a softwood type will 
probably be an impossibility, efforts 
should be made to utilize or dispose of 
as much of the hardwoods as possible 
to liberate higher proportions of soft¬ 
woods. 
In hardwood mixtures balsam is 
most susceptible as a free tree and 
white spruce as an overtopped tree, 
which demands early cutting of free 
balsam and early liberation of over¬ 
topped white spruce. The spruces, 
particularly white spruce, should al- 
