40 



BITLLETIN 871, U. S. DEPAETMENT OP AGRICULTURE. 



Typical frost cracks are rarely found except on large trees. Table 

 VII shows the percentage of frost cracks on the trees analyzed. 



Table VII. — Incense-cedar trees found in the combined areas having frost cracks. 





Locality. 



Number 

 of trees 

 (basis). 



Trees with frost cracks 

 (per cent). 





Open. 



Internal. 



Total. 





509 

 566 



4.12 

 1.41 



3.14 

 .53 



7.26 





1.94 











1,075 



2.70 



1.77 



4.47 







Here again, as in the case of fire, the wounding is worse on the 

 intermediate than on the optimum area. The percentage of trees 

 exposed now or in the past to inoculation by fungous spores through 

 the medium of frost cracks is rather low and not of great importance 

 on any of the areas. Frost cracks in incense cedar are not nearly so 

 prevalent as Meinecke (16, p. 31) found for white fir. 



LIGHTNING. 



Incense cedar suffers only slightly from injury by lightning. This 

 is to be expected, since the dominant species in a stand and as such 

 the taller trees (25, p. 36) are most subject to lightning stroke, while 

 incense cedar rarely attains this position in the mixed stand in which 

 it is found. Plumnier (25, p. 33) also shows that incense-cedar wood 

 is a poor conductor of electricity. 



An incense-cedar tree in the forest badly shattered by lightning 

 is an exceedingly rare sight and immediately provokes comment. 

 However, trees with slight lightning injuries are more common. 

 Such injuries show as superficial wounds on the trunk. Often the 

 wood is not scarred, but the bark and cambium are killed. The 

 bark then drops away, exposing the sapwood, which in turn dries 

 out and checks, offering fungous spores access to the heartwood. 

 Long wounds extending spirally around the tree, so common in White 

 and red fir in this region, are an unusual occurrence on incense cedar. 



Table VIII indicates the prevalence of lightning scars. 



Table VIII. —-Incense-cedar trees found on the combined areas having lightning scars. 





Lo< ality. 



Number 

 of trees 

 (basis). 



Trees with lightning scars 

 (per cent). 





Open. 



Internal . 



2.53 

 1.06 



Total. 



Intermediate area 



509 



560 



1.76 



3.54 



4.31 



4.60 











1,075 



2.70 



1.77 



4.47 









