DEFECTS IN TIMBER CAUSED BY INSECTS 



37 



follows in recovering trees. In fir trees one, two, or three rings may 

 fail to form completely around the stem, particularly at the base, 

 and are represented only by partial arcs (fig. 36) (48). 



Rings of traumatic resin ducts are frequently deposited in the 

 terminal portions of defoliated fir trees during the first to third 

 years of feeding. 



Complete defoliation of certain hardwoods in the early spring 

 produces a double ring the same year. These defects result in a 

 great loss of increment, increasing the rotation from 3 to 10 years, 

 and cause confusion in growth studies based on the annual rings. 



Similar distortions of rings are found in Douglas fir, due to de- 

 foliation by the spruce bud worm, and in western fir, spruce, yellow 

 pine, and particularly 

 lodgepole pine, due to 

 defoliation by the nee- 

 dle miner. 30 



Such losses and de- 

 fects can be prevented 

 only by the prevention 

 of "defoliation, a prob- 

 lem of forest manage- 

 ment. 



DEFECTS CLASSED AS 

 PITCH POCKETS AND 

 PITCHY TIMBER 



Pitch pockets are 

 openings between the 

 grain of the wood 

 which contain more or 

 less pitch or bark. 

 They are graded as 

 small, standard, and large pitch pockets. These pockets range 

 from one-eighth inch to 2 inches in width and from 3 to 12 inches 

 in length. Sometimes, instead of pockets, there are merely pitch 

 streaks. These defects may be caused by insects as well as other 

 agents. 



The pockets are small, usually about one-half to 1 inch in length, 

 and about one-half inch in width, full of pitch; in pine, they are 

 parallel to the grain. Sometimes they are as large as 2 inches in 

 diameter and contain a large quantity of pitch. This injury may 

 be caused by unsuccessful attacks of bark beetles 31 which have failed 

 to kill the tree and have been drowned out by the flow of pitch. 

 (Fig. 37.) It is a sound defect which can be prevented only by con- 

 trolling the bark beetles that attack the living trees. 



Excessive pitchy streaks in yellow and other pine lumber are 

 sometimes caused by the larvae of a moth 32 working in the cambium 

 (fig. 38), especially in mature trees. 



Fi( 



40. — Gum spot in Douglas fir, caused by 

 headed borer (Melanophila d) ummondi) 



30 Recurvaria milleri Busck. 



31 Dendroctonus spp. The term "pitch pocket" is here used to define what is appar- 

 ently the tree's further means of defense from attack by bark beetles, after the pitch 

 running out of the entrance hole, forming a pitch tube, has failed to drown out the 

 beetles. 



32 Pinipestis zimmermanni Grote, the Zimmerman pine moth. 



