COVER TYPE AND FIRE CONTROL yak 
INCENDIARY CAMPERS 
pie AND UNKNOWN FIRES LIGHTNING FIRES 
GRASS 
CHAPARRAL 
WOODLAND penne ees \// 
ee ———-- 
BRUSH sea ese UMMM 
OO 
YELLOW PINE nee BEEN Ro 
DOUGLAS FIR 
MIXED CONIFER 
SUGAR PINE-FIR 
FIR BEE UL mpegs au 
ween 6 i j tes BS Ss ee ee ea Se 
eeone Pied ees 
50 40 30 20 10 0) 10 20 30 40 
NUMBER OF FIRES PER 100,000 ACRES 
FIGURE 6.—Number of general-risk fires per 100,000 acres annually, by types, 1911-1920 
Among the principal timber-type groups, Douglas fir has 88 per 
cent as many man-caused fires as the western yellow pine and mixed 
conifer group, and the sugar pine-fir and fir group but 44 per cent as 
many. Given equal opportunities for fires to start from human causes, 
a ratio, similar to that for the lightning fires, of 81 per cent between 
the pine and fir groups would be expected. Evidently, since this is 
not the fact, the total human use within the fir is distinctly lower than 
in the pine belt. This view is confirmed by the fact that in August, 
when the susceptibility of ail types to starting of fires most nearly 
approaches equality, only 55 per cent as many man-caused fires start 
in the fir asin the pme. No detailed comparison of seasonal distribu- 
tion of lightning and man-caused fires is required, since the two groups 
have such different seasonal histories. 
TABLE 9.— Average seasonal disiribution of man-caused general risk fires (incendiary, 
camper, unknown), by types, 1911-1920, 12 timbered forests 
[Number of fires per 100,000 acres] 
Type Mer.| Apr. | May | June | Juiy | Aug. | Sept. | Oct. | Nov.| Total | Ratio 
Western yellow pine___________ 0.42 | 0.44 | 0.92 | 2.70 | 6.66 | 10.56 | 7.05 | 4.59 | 0.79 | 33.53 |_-__._ 
Maxediconiferes\-) 4225-0. SOGE|P 1s 26r) L840 e |) 2. Ge 6s Hla710, 622) © QABIA a7 S35 Poo soa 
WOU CAS fire ke es. ee BBS 628 SOB oO \) GEO2F | SE G4] SB aE Sale a Sak ee) 88 
Suparipmectire es.) ere So tee ee PL N26 442 ale G4) Setoeu 2295) || 66319 79h) Be 
sir eames arty pe Mien ie TS De IL oligo 19 67 | 2.43 5. 60 3.95 | 1.46 3247) 14054) )o222 3. 
GTS oe in ol ee Br nae | MO . 36 .99 | 2.34 | 6.49 6. 31 5.40 | 1. 26 230 | 20,42, |-2- 22 2 
@haparraley pear et ee a Sei ess. ee 1.24) 2598 | 8544 | 16.135) 21016-) 6595 | 1524 | 48.414 |-223 = 
WiOOdl an Gee soe mie PE -21 | .42 | 1.79 | 4.00 |. 7.78]. 5.15 | 1.68 | .32 | 21.35 |_-___- 
STS Me pee eee BS -05 <2 94 | 1.35 | 4.07 9. 92 7.60 | 4.48 -45 | 29.13 81 
"AWVCLAGOY- Meee se 17 oot 90 | 2.07 | 5: 25 9. 72 7.18 | 4.63 OUR oO soe |eeeoee 
SUMMARY OF TYPE GROUPS 
Western yellow pine, mixed 
conifer groups. 222k. files: 
Sugar pine-fir, fir group_____-__- 
Grass, woodland, chaparral 
0. 24 | 0.35 | 1.12 | 2.78 | 6.33 | 10.60 | 7.97 | 5.88 | 0.81 | 36.08 100 
ee ee | is Se -19|} .80} 2.86} 5.83] 3.86] 1.79 | .43 | 15.76 44 
peers -19 | .52) 2.05 | 5.32] 7.68} 4.87] 1.54] .66 | 22.83 63 
