INSECT ENEMIES OF WESTERN FORESTS 



(This loss is for the most part counterbalanced by new grot\"th.) 

 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 e x t e n t 

 that long periods are 

 required for replace- 

 ment (fig. 2). An- 

 nual loss by forest 

 insects in the West- 

 ern States, includ- 

 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 lightning or 

 windstorms. On the 

 other hand, much of 

 it can be prevented 

 through silvicultural 

 practices, proper for- 

 est management, and 

 direct control meas- 



Figure 2. — Not fire but bark beetles destroyed this basiu 

 •J-i-^^O' 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 western 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 period 1921-31. Growth during the 

 same period, which, owing to drought and to defoliation by the 



