20 BULLETIN 1060, LV S. DEPARTMENT OF AGRICULTURE. 



to heal over scars or wounds along the bole ; here the spores of fungi 

 soon establish themselves and, on account of the very moist condi- 

 tions in spruce stands, cause the rapid decay of much sound wood. 



Advance rot spreads quickly in this species, and, though often 

 hard to detect, it becomes very noticeable after lumber is dried. It 

 is commonly, though not always, accompanied by a change of color 

 in the wood, appearing as streaks of red, yellow, or green. Tests 

 were made recently by pathologists to show the effect of different 

 stages of decay on the strength of the wood, particularly for spruce 

 airplane stock, but these data are not yet available for publication. 



INSECTS." 



Although Sitka spruce, like other forest trees, is subject to insect 

 attacks, it is not so susceptible as most of its associates in the forests 

 of the Pacific coastal region. The attacks are naturally more serious 

 in pure or nearly pure stands of Sitka spruce than in stands in which 

 it occurs in mixture. Damage is caused by three classes of insects — 

 bark beetles, defoliators, and borers. The first two classes attack 

 standing timber and the last works in felled trees. 



The most important insect enemies of Sitka spruce are the bark 

 beetles, of which the most destructive is the Sitka spruce beetle 

 (D endroctonus obesus). This beetle attacks the living trees and 

 kills them by girdling in the cabium layer. In attacking the trees 

 the first broods enter the inner bark of the middle trunk, and those 

 which appear later extend the infestation to the base of the trunk 

 and even to the larger roots. This beetle also works in the inner 

 bark of stumps, logs, and slash of felled trees. Although no exten- 

 sive depredations of the Sitka spruce beetle have been found thus 

 far, it has been reported now and then that groups of Sitka spruce 

 have been killed by its activity. If infestations should ever become 

 widespread it would be possible to practice control operations by 

 cutting and barking the infested trees before the beetles emerge irp 

 the late spring. It would not be necessary to burn the bark in this 

 work. 15 



From time to time Sitka spruce is subject to the attacks of such 

 defoliators as caterpillars, sawfly larvae, and aphids, all of which 

 destroy the needles and may therefore occasionally kill trees over 

 large areas. In Clatsop County, Oreg., in 1890 and 1891, Sitka 

 spruce and western hemlock were attacked and killed over an area 

 of thousands of acres by a caterpillar belonging to the Geometrid 

 family. During the years 1917 to 1920 the Sitka spruce and western 

 hemlock on several hundred thousand acres on the Tongass National 



14 Prepared in collaboration with Forest Examiner A. J. Jaenicke, U. S. Forest Service. 



15 For detailed information regarding control measures, see Bulletin 83, Part I, " Bark 

 Beetles of the Genus Dendroctonus," by A. D. Hopkins, Bureau of Entomology, IT. S. De- 

 partment of Agriculture. 



