INSECT ENEMIES OF WESTERN FORESTS 5 
(This loss is for the most part counterbalanced by new growth.) 
On the other hand, epidemic insect outbreaks occurring from time to 
time definitely de- 
plete the forest capi- 
tal over large areas 
to such an extent 
that long periods are 
required for replace- 
ment (fig. 2). An- 
nual loss by forest 
insects in the West- 
ern States, imcelud- 
ing depredations on 
standing timber and 
damage to logs,sawed 
lumber, and finished 
wood products in use, 
is variously estimated 
at from $20,000,000 
to $100,000,000. 
A considerable por- 
tion of this loss is as 
unavoidable as losses 
from lghtning or 
windstorms. On the 
other hand, much of 
it can be prevented 
through silvicultural 
practices, proper for- 
est management, and 
direct control meas- 
Ficurp 2.—Not fire but bark beetles destroyed this basin 
ures. of lodgepole pine in Yosemite National Park. 
DIRECT LOSSES 
In the mature timber stands of the West the largest single item of 
insect loss results from activities of bark beetles. Surveys indicate 
that these pests destroy annually 1 billion to 5 billion board feet of 
mature timber in our westerir forests. 
A survey made in California in 1931 indicated that losses of mer- 
chantable timber due to bark beetles in that year totaled about 1,250,- 
000,000 board feet, which represents a loss of nearly $3,000,000 in 
stumpage values, aside from the regional asset represented by the 
manufacturing value of the lumber. 
In southern and central Oregon, during the 10 years ended with 
1934, the western pine beetle caused a net depletion of the ponderosa 
pine stands (fig. 3) amounting to 2,240,000,000 board feet. A typical 
section in the Klamath Indian Reservation, carrying a stand of 
11,074,000 board feet in%1921, lost 3,875,000 board feet through bark- 
beetle attack’ during the 11- ~year per iod 1921-31. Growth during the 
same period, which, owing to drought and to defoliation by the 
. 
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