INSECT ENEMIES OF EASTERN FORESTS 5 
Defoliating insects likewise destroy considerable bodies of mature 
timber. These outbreaks, however, usually appear at rather long 
intervals and are of comparatively short duration. An exceptional 
instance is that of the spruce budworm in the Northeastern States and 
Canada, which ravaged the spruce and fir forests for a period of about 
10 years (from 1910 to 1920). It has been estimated that in the spruce- 
fir types of Maine, Ontario, Quebec, and New Brunswick from 40 to 
70 percent of the timber was destroyed and that the equivalent of more 
than 25 years’ supply of pulpwood for current annual American paper 
requirements was lost. 
Certain species, even if they do not kill the timber, cause a cessation 
or retarding of growth, which may increase the rotation period of the 
stand from 5 to 10 years or more. Such defoliations may be local and 
may be confined to only a single species of tree, or they may spread over 
enormous areas, involving several species. The most recent outbreak 
of the pandora moth in the ponderosa pine stands of southern Oregon 
occurred between 1918 and 1925 and covered approximately 400,000 
acres. Growth measurements from plots in this area showed that for a 
period of 11 years the normal forest growth on this area was reduced 
an average of 32 percent, or a loss of increment of approximately 100 
million board feet. The weakening of these trees was followed by 
heavy loss from bark beetles which killed as much as 30 percent of some 
stands. Hopkins (230, 231); Swaine, Craighead, and Bailey, 1924 
(403 3); St. George and Beal (371), Peirson (350), and/the United 
States Bureau of Entomology (417), have given valuable information 
on the injury to standing timber. 
LOSSES FROM FOREST INSECTS 
Various attempts have been made to express in monetary values the 
annual loss occasioned by forest insects. Such estimates must of ne- 
cessity be based on inadequate data. For the most part, it is necessary 
to use information based on special cases and apply it with modifi- 
cations to the whole field. In only a few instances has it been possible 
to obtain a fair sampling of the entire timber supply subject to damage. 
That the combined losses in all timber resources of the United States 
for the wood-using industries and for park and shade trees must be 
very large is indicated by the preceding examples of specific losses. 
On the other hand, it must be borne in mind that in the case of mature 
forests many insect outbreaks occur in out-of-the-way places, where 
the timber will not be accessible or merchantable for 25 to 50 years 
or more, and consequently the losses there will be largely offset by new 
growth before the stand can be utilized. 
For a number of years systematic surveys have been conducted over 
considerable areas, especially in the mature timber stands of the 
Western States. From these, a fair sampling of the supply and of 
the losses from bark beetles makes possible a very accurate estimate. 
The killed timber has amounted to from 1 to 6 billion board feet, an- 
nually, which at a stumpage value of at least $3, would represent up to 
20 million dollars. 
Detailed estimates of the losses caused by the southern pine beetle 
in the East have never been available because of the scattered owner- 
ship of the timber, but the stumpage value of the pine killed in the 
last 50 years probably exceeds $50,000,000. 
