2 BULLETIN 1495, U. 8S. DEPARTMENT OF AGRICULTURE 
All these are intimately related, and they must be understood before 
the protection organization and the actual control of fire can reach 
a satisfactory level of effectiveness. 
Cover type, or the typical tree or brush species or group of species 
occupying a given area at the present time, is clearly an element of 
basic importance in fire control. This was brought out in earlier 
work by the authors,’ in the course of a study mainly confined to 
methods and costs of ‘protection. It is demonstrated more pointedly 
by Sparhawk’s pioneer work? which employed similar basic data 
for all of the western national forest districts for the years 1911 to 
1915. His contribution has laid down a method of attack which 
will be increasingly applicable as more complete and accurate informa- 
tion on each fire is systematically collected. His statement that ‘‘the 
only scientific basis for such a study is what has actually happened ; 
that is, the actual fire history of the different forest areas’’ is clearly 
sound and is the foundation of this circular. However, the varia- 
bility of individual fires is so great, and the classification of type and 
hazard classes so incomplete, that even with records for a 10-year 
period available, the authors have not felt justified in attempting 
the complete analysis proposed by Sparhawk. 
The present study aims to distinguish the occurrence and behavior 
of fire in the major cover types as a basis of fire control, by means of 
average figures derived for each of the major types, showing length of 
season, prevalence of fires, rapidity of spread, and difficulty of control. 
These will express in preliminary fashion the relative effectiveness 
of equal protection effort in each of the types, and will explain pre- 
viously observed differences in results obtained in different national 
forests and variations in behavior of fire from different causes. 
COVER TYPES OF NORTHERN CALIFORNIA 
DEFINITION AND DISTRIBUTION 
The region studied is one of varied and roughly broken topography 
with a great range in elevation varying from 1,000 feet above sea level 
in the valleys to 14,000 feet at the crest of the Sierras. Cover type 
consequently varies enormously. The nine major cover types 
employed in this study are those used in national-forest administra- 
tion. (Table 1.) They may be summarized briefly, as including 
(1) the western yellow pine type, of which western yellow pine (Pinus 
ponderosa) is the principal tree (pl. 1, A), and (2) the mixed conifer 
type, in which western yellow pine grows in mixture with sugar pine 
(P. lambertiana) and in which Douglas fir (Pseudotsuga taxifolia), 
incense cedar (Libocedrus decurrens), and white fir (Abies concolor) 
occur as associate trees in varying proportions (pl. 1, B). Douglas 
fir (8) also occurs as a distinct type. (Pl. 2, A.) The sugar pine-fir 
type (4) is composed of white and red fir (A. concolor and A. mag- 
nifica) In mixture with sugar pine. In some places the Jeffrey pine 
(Pinus jeffreyi) takes the place of the western yellow pine in the stands 
or may grow with it in mixture with other species. The pure fir 
type (5) includes white fir, mixtures of white and red firs, and the 
red fir alone. (Pl. 2, B.) Within the timber belt a temporary 
2SHow, S. B., and KoToxk, E. I. FOREST FIRES IN CALIFORNIA, 1911-1920: AN ANALYTICAL STUDY. 
U.S. Dept. Agr. Gire: 243, 80 p., illus. 1923. 
3 SPARHAWE, W. THE USE OF LIABILITY RATINGS IN PLANNING FOREST FIRE PROTECTION. Jour. 
Agr. Research 30: 93: -720, illus, 1925, 
"SPs 
