THE GENUS DENDROCTONUS. 



Ill 



EFFECTS ON COMMERCIAL VALUE OF THE WOOD. 



The commercial value of the Douglas fir trees killed by the beetle 

 is not seriously impaired for several years after they die, except that 

 the sap wood discolors and otherwise deteriorates, but the heart wood 

 of large trees may remain sound for twenty years or more. On the 

 other hand, if they are seriously attacked by wood-boring insects 

 the wood may deteriorate rapidly. 



FAVORABLE AND UNFAVORABLE 

 CONDITIONS FOR THE BEETLE. 



Favorable conditions for 

 the multiplication and de- 

 structive work of this bark- 

 beetle are found in the drier 

 regions, where the growth of 

 the trees is slow and where 

 the older trees are frequently 

 injured by fire, storms,. land- 

 slides, etc., as also in the 

 more isolated sections of the 

 forests in such a region where 

 no continued timber-cutting 

 operations are carried on. 

 Unfavorable conditions for 

 attack on living timber are 

 found in moist regions, where 

 the growth of the trees is vig- 

 orous, as in the coast, Cas- 

 cade, and Sierra sections of 

 Washington, Oregon, and 

 California, and especially in 

 those sections in which con- 

 tinued timber-cutting opera- 

 tions are carried on under a 

 system of lumbering or forest 

 management which requires 

 that the matured or older 

 timber, as well as that which 

 is dying and " beetle infested/' be taken out, and where the younger, 

 vigorous timber is protected from injury by fire and other causes. 



METHODS OF CONTROL. 



Whenever in a given locality it is positively determined that this 

 species is attacking and killing the Douglas fir, bigcone spruce, or 

 western larch, and that the bark of living and dying trees contains 



Fig. 68.— The Douglas fir beetle: Section of log with bark 

 removed, showing brood galleries marked and grooved 

 on surface of wood. (Author's illustration.) 



