40 
BULLETIN 8*71, IT. S. DEPARTMENT 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. 
Intermediate area 
509 
566 
4.12 
1.41 
3.14 
.53 
7.26 
1.94 
Combined 
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. Plummer (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. 
Locality. 
Number 
ol trees 
(basis). 
Trees with lightning scars 
(per cent). 
Open. 
Internal . 
Total. 
509 
566 
1.76 
3.54 
2.53 
1.06 
4.31 
Optimum area . . ----- 
4.60 
Combined 
1,075 
2.70 
1.77 
4.47 
