24 BULLETIN 1495, U. S. DEPARTMENT OF AGRICULTURE 
is not so striking as that for some of the other elements of the problem, 
and does not aficct materially the reliability of the figures based on 
total type areas. 
TaBLE 11.—Risk areas, by types, northern group of forests, all causes, 1911-1920 
Type Total Area Ratio 
area of risk of risk 
1,000 acres|1,000 acres} Per cent 
BRine7eTOUD so! 3 Ree 3 A ee ER oe ebay Ue oe Seema Ak is eee 2, 819 1, 205 43 
DOUG aS Mir ke CAF SARS NN a RTS 8 ARs LO EISEN IES NES Sh tral cara 1, 101 453 41 
WEES fg 0) B yO eee ee eee gee, ange lee AnD nce A RN UN Se cat age 671 265 39 
Totalstimbered ss Ses eee OE Eee Tees eae Pee Mee 4, 591 1, 923 41.9 
Brush Cha parra ley Se fhe tl yes 2 Re Ne as aN Rah ho ae Ree A, ge 1, 303 598 46 
GUISES OO Chiba i Usk a a Ml a A a Shan SN ye ee As eee ee 353 174 49 
Rotal. nOnEtM Mere Cosy aely he Gee ee ee RES Seep a) ER 1, 656 | 772 | 46.6 
AUltty pes s=t a. Se Bd ae ee 6, 247 2, 695 43.1 
CONTROL OF FIRE AS AFFECTED BY TYPES 
The effectiveness of control over a period of years 1s gauged indi- 
rectly by the percentage of fires over 10 acres in extent, or C fires, 
and more directly by the size of the average fire and the percentage 
of area burned annually. (Table 12 and fig. 7.) Of the general-risk 
fires only, the proportion of C fires averages highest (57.1 per cent) in 
the chaparral type, considerably lower in the brush, grass, and wood- 
land types, and so in descending order through the Douglas fir, 
western yellow pine, mixed conifer, and sugar pine-fir, down to 9.9 per 
cent in pure fir. The size of the average fire, ranging from 539 acres 
in chaparral to 29 acres in the fir type, decreases in almost the same 
order. The largest average C fire is found, as might be expected, in 
the chaparral type and the smallest in the fir type. 
RESULTS OF PROTECTION 
The success of protection as measured by average annual percentage 
of the type burned in general-risk fires (Table 12, last column) has 
been least in the chaparral and brush types, or those with the greatest 
amount of inflammable fuel and with the most critical climatic con- 
ditions. Within the commercial timber types the least success has 
been attained in the western yellow pine and Douglas fir types and 
the greatest success in the pure fir. As the highest present exploitable 
timber values per acre are in the pine types, particularly in the western 
yellow pine, and the lowest in the fir type, even if the objective of 
fire control is considered to be merely preservation of existing values, 
the effort made during the decade has by no means accomplished its 
purpose. ‘The heaviest losses have been sustained in the forest 
types of highest present values. 
The situation m the restocking brush fields is particularly grave, 
because the annual rate of loss of 1.24 per cent means that the process 
of restocking the brush fields themselves is retarded through burning 
of newly established reproduction and by reduction of site quality; 
also because all fires originating in the brush tend to wipe out a part 
of the adjacent timber belt. The annual loss rate of 3 per cent in 
chaparral likewise is to be regarded as serious, for as has already 
