ROLE OF FIRE IN CALIFORNIA PINE FORESTS 7 
in 1919, in order to follow the formation of new scars and the exten- 
sion of old ones. In 1923, as a result of two successive burns 8 of 
the 72 originally unscarred trees (or i1 per cent of the total trees in 
this class) had developed new fire scars. A study of the detailed 
notes of each tree shows that in most cases the new scars were formed 
where a down log or a heavy accumulation of débris against a tree had 
burned. While these figures are not to be regarded as conclusive in 
showing the average rate of formation of new scars, they are signifi- 
cant in proving that even the very lightest fire, such as this was, 
may result in the formation of new scars because of intense heat 
developed locally in the course of the burning. 
Of the trees on this area originally scarred and reached subsequently 
by fire, 5 per cent were burned down, 8 per cent were killed by other 
causes, 5 per cent formed new scars without enlarging the old ones, 
71 per cent showed extensions of the original scars, and only 11 per 
cent showed no extension of the oldscars. On only 13 percent of the 
scarred trees which survived the fires were the scars not enlarged. 
This light-burning study showed the average dimensions of the 
original scars on 95 of the trees to have been: Width, 2.01 feet; height 
4.5 feet; area 4.52 square feet. 
As might be ene, the extension of the scars after the two fires 
was mainly upward. This isshown by the new measurements, which 
were: Width, 2.56 feet; height, 5.25 feet; area, 6.72 square feet. 
The average increase in scar area thus amounted to 48 per cent, 
as shown in the following extension figures: Width, 0.55 foot; height, 
0.75 foot; area, 2.2 square feet. 
The magnitude of the extension of a scar depends in the main on 
the size of the original scar, for the larger the surface area burned 
the longer continued and more intense will be the heat released in 
the new burn. The tendency toward acceleration in this form of fire 
damage points to a law that will be found true in most forms of fire 
damage. That is, a process of loss from fire once started gathers 
momentum with each succeeding fire and finally results in total loss 
of the individual tree or of the stand. 
SUSCEPTIBILITY OF VARIOUS SPECIES TO FIRE SCARRING 
The following percentage figures, based on open fire scars and re- 
ported by Lachmund (14), give an indication of the relative suscep- 
tibility of the important species to fire scarring: Incense cedar 61.5 per 
cent, western yellow pine 42.7 per cent, sugar pine not given, white 
fir 25 per cent, and Douglas fir 17.2 per cent. 
On the Snake Lake plot the figures are: Incense cedar 72.2 per 
cent, western yellow pine 51.2 per cent, sugar pine 54.95 per cent, 
Douglas fir 40.5 per cent, and white fir 15.1 per cent. det 
The two sets of data agree in a genera] way in showing incense 
cedar to be the most susceptible species, the two firs the least sus- 
ceptible, and the pines intermediate. On the Snake Lake area the 
low rate of scarring on the firs is due largely to the fact that these 
species generally grow on the northerly slopes where fires have been 
less frequent than on the drier aspects where the pines and cedars 
are more abundant. The inflammability of incense cedar bark is 
largely responsible for the susceptibility of this species, the bark of 
the firs and pines burning very much less readily. 
