COVER TYPE AND FIRE CONTROL 7 
during the same month. Thus even at the peak of the fire season the 
high-elevation timber types do not dry out to the degree that the 
western yellow pine type does. The litter in the fir type becomes dry 
enough so that fires start readily but do not spread as rapidly as in 
the western yellow pine and are more readily controlled. Direct 
measurements of litter moisture are so fragmentary that the differ- 
ences between types are by no means certain. Those available indi- 
cate that for the period from June to October the moisture of the 
litter in fir and sugar pine-fir types was higher than the danger point 
(8 per cent) 40 per cent of the time, as compared to 29 per cent of the 
time in the western yellow pine and mixed conifer types. 
TABLE 3.—Seasonal and annual rainfall and length of rainless season at northern 
California stations } 
Sea- 
An- sonal | Dura- 
Period of} nual | precip-| tion 
record |precip-! itation | of dry 
: itation | May to) season 
October 
Type Station 
Inches | Inches | Days 
123 
Grassi ainteeets Are ic se Seemene Va (2 stations) ____| 1874-1923 29.01 2. 65 
@ NAAT As ee ees ee Mokelitmire: Hales =) 3 2 ee Se 1882-1922} 33.18 3. 68 122 
ShinvlesSpringss 2 2a eee ees 1849-1912 
Woodlands ein 2a ee Sate Sonoracc 2 ae tee ae Bee as 1887-1922} 35.02 4,51 121 
Western yellow pine_____________ Wlacervillee 222e eV re eeee 1874-1922 
Georsetowhis ss eae 1872-1923} 51.30 6. 43 108 
GrassaV alley 2: ees ns et ee 1872-1923 
INGvada? City 22-3 ta eee 1863-1923 
Maxed conilerss- es Sos CIS CORSE sete 2 re eae ee Set 1870-1916 | 51.56 7. 03 105 
ees Sip speach, lity ps Ppa peer biaNE 5 1870-1923 
POWaT Hills oe. Peewee re Aree 1879-1910 
North ealoes aid SS! eee 1870-1923 
; Baaieran GG phere ae ee eee 1888-1923 
a thy) a Se Se Secs ee Se ee SMM Eee eh pe ee eee 1870-1923 | 59.93 8. 26 87 
IB OWANANIS ATs a ee ne 1871-1916 
a summary of the climatological data for the United States, U. S. Weather Bureau Stations 14 
and 15. 
The long-period records of the United States Weather Bureau 
(Table 3) show that total annual precipitation is least in grassland 
(29.01 inches), followed by that in the chaparral and in the woodland, 
with a substantial increase of approximately 22.5 inches in the western 
yellow pine and mixed conifer, and a further increase of over 8 inches 
in the fir type. Thus the total precipitation at higher elevations 
(59.93 Ebon | is over twice as great as in the grasslands of the foot- 
S. 
Of even greater importance from the standpoint of fire control is 
precipitation during the fire season (May to October, inclusive). 
The quantities rece:ved range from 2.65 inches in grassland to 8.26 
inches in fir, or over 300 per cent, following the same order of types as 
for total precipitation. 
The length of the fire season, as well as the ease of start and spread 
of fires during that time, are determined quite as much by the dura- 
tion of the rainless season as by the total annual precipitation. The 
average length of rainless season as given in Table 3, ranges from 
about 122 days for grass, chaparral, and woodland to 87 days for fir. 
This, when coupled with the temperature differences and the greater 
total and seasonal precipitation already noted, explains the shorter 
fire season at the higher elevations. 
