ROLE OF FIRE IN CALIFORNIA PINE FORESTS 21 
land. On the burn the infestation was found to be excessive. On 
one 40-acre tract, a total of 55 trees, both western yellow and sugar 
pines, were peeled by the crews. Over the entire burn the infestation 
_was strikingly heavy; and on one acre 7 infested trees were found 
and peeled. That the insects had entered the trees after the fire, was 
definitely established by the presence of fresh pitch tubes overlying 
the burned bark. The adjacent unburned area had nothing like the 
same degree of infestation. A cruise of one 40 showed 3 infested 
trees, while another 40 had 5. This striking contrast between the 
burned and unburned forest is still further heightened by the data 
obtained in a later inspection made in July, 1917, about three months 
after the completion of the control work. At that time it was found 
that on the 40-acre tract where the 55 trees had been treated 10 
additional trees were infested. 
That these examples are not exceptional is shown by the results of 
fire-damage studies on many other large burns. An increase in 
infestation on all the areas studied has been found without exception, - 
the only variation being in the relative intensity of the attack. It 
appears to be established beyond contradiction that serious loss from 
insects is a corollary of fire, whether that fire be light, as in the case 
of the Snake Lake and Mormon Hill burns, or heavy, as on the Crane 
Valley burn. The indications are that the extent of this damage is 
likely to be from 8 to 12 times as great as that existing before the 
fire, and that heavy loss from insects will continue for about two 
years after the fire. Without attempting to state an absolute aver- 
age figure of loss for insect damage after fires, it may be pointed out 
that on the areas studied the stand suffered to the extent of about 
1,000 board feet an acre. This form of loss, therefore, is serious. 
Loss from insects following fires is one of the several factors which 
normally result in the gradual depletion of the forest stand. None of 
these factors, except occasionally heat killing, results in wiping out 
the forest at one stroke; but all combine to make any extensive fire 
in the virgin forest the starting point of a train of circumstances the 
full effects of which do not become apparent for years. 
Why wsect attacks follow fire—Just how insect infestations take 
hold in a forest. so rapidly immediately after a fire is difficult to ex- 
plain. A study conducted at the Feather River Experiment Station 
ae “— 
throws some light on this question. In the fall of 1916 a fire burned 
a strip through a dense stand of western yellow pine poles, injuring 
many of the trees, chiefly by partially killing the crowns. A year 
_ after the fire a detailed study was made of many of these trees to 
tation. Oft 
determine, if possible, what influence the fire had had on insect infes- 
< trees uninjured by fire, 1.5 per cent had been heavily 
_ attacked by Dendroctonus brevicomis, but an abundant flow of pite 
_ repelled the beetles. Of the trees injured by the fire, 60 per cent had 
_ been successfully attacked and had succumbed. ‘This is the more 
_ remarkable since thrifty young trees are practically immune to attack. 
_ Trees whose vigor had been lowered through crown injury were prom- 
_inent among those successfully attacked, and this fact mdicates 
clearly that any serious reduction in the vigor of a tree predisposes 
it to attack by insects. 
_._ Loss of vigor by partial killing of the crown is not the only form 
of injury that invites insects. Fire scars on the trunk are a favorite 
place for attack... A detailed examination of the injured trees showed 
