18 BULLETIN 1495, U. 8. DEPARTMENT OF AGRICULTURE 
To build up the regular force in proportion to the number of fires—a 
practice which has been tried—has the effect of requiring each man to 
cover an area larger than his usual district. Speed in reaching fires is 
therefore reduced below the point of safety. 
DISTRIBUTION OF FIRES BY TYPES 
_Each type (Table 5) starts with a low number of fires in the early 
season, rises to a peak in August, then drops sharply. In total 
number of fires for the season per 100,000 acres of each type, the 
mixed conifer leads, followed in order by western yellow pine, chapar- 
ral, Douglas fir, brush, fir, and sugar pine-fir, with grassland and 
woodland lowest, the difference between mixed conifer and woodland 
representing an extreme range of 48 fires. When the types arear- 
ranged in natural groups (fig. 5), significant expressions of the com- 
parative total risks are obtained. In the first timbered group con- 
taining the western yellow pine and mixedconifer types, the risk is 
72.44 fires; in the Douglas fir type, the risk is 53.03, and in the third 
eroup, containing the sugar pine-fir and fir it is 45.40. With the 
figures for western yellow pine and mixed conifer as a base or 100 
per cent, the values for the other types can be expressed as percent- 
ages. (Table 7.) Of the timbered types, the fir group has but 63 
per cent as many fires per 100,000 acres as the pine types. 
TaBLE 7.—Data in Table 5 summarized and expressed as percentages of western 
yellow pine-mixed conifer group 
Types May | June | July | August peer Gato, Total 
Micedicmten © ieee ee fy 9G) | {°A00)) 100) noes Te ee 100 
Sine plnemnc te 0) Coe ETT | oO Nia i ac eel pe 
Se aa Siar es } 22 31 64 86 58 33 63 
Bean Es oy 080 | re ar ea 
Woodend’ 2 uc ep ee ag Bol et ee 
The fir and sugar pine-fir types, beginning in May with only 22 
per cent as many fires as the western yellow pine and mixed conifer 
eroup, rise steadily to 86 per cent as many fires in August, and then 
drop to 33 per cent in October. Thus even at the peak of the fire 
season in August the absolute chance of fires starting from all the 
general-risk causes 1s somewhat lower in the fir group. Before that 
time the slower drying out of the fir types probably prevents fires 
from starting, which, with an equal opportunity, would start in the 
pine type. The Douglas fir type, with 75 per cent as many fires as 
the pine for the season, is generally in an intermediate position be- 
tween the pine and fir groups. 
In seasonal total the chaparral and brush group has 69 per cent 
as many fires as the pine group. The fact that, in September, the 
number of fires in the brush is 89 per cent as high as in the pine, is 
probably explainable by the number of incendiary fires set at this 
time of the year, which, as shown elsewhere, are largely concentrated 
in the brush types. 
