TIMBER GROWIXG AND LOGGIXG PRACTICE lis' CALIFORNIA 47 
MIXED TYPES 
After an analysis of timber survey data for several townships, it 
was found that in progressing from the dry lower edge of the timber 
belt in the pure yellow pine type to the relatively moist fir types of 
the upper belt, the number of small seed trees gradually increased. 
(Fig. 19.) In the yellow pine type the average number of 18 and 20 
AVERAGE NUMBER OF SEED TREES PER ACRE 
! 2 3^56 
Fig. 19. — These are the trees 12 to 20 inches in diameter that would be left by the appli- 
cation of a 20-inch cutting limit in the important timber types. The significance of 
the avei-ages given above is made cleai- in Figures 18 and 20 
inch trees per acre is 1.6; in the yellow pine-sugar pine type, 3; 
in the yellow pine-Douglas fir type, 3.6 : in the mixed conifer type, 
3.9 ; in the sugar pine-fir, and also in the yellow pine-white fir t^^pes, 
4.2 ; and in the group of fir types (white fir, white and red firs, and 
red fir), 6.4. If averages told the entire story, we might conclude 
that all types except the yellow pine are fairly adequately provided 
with seed trees. But it is worth while to go a step farther and 
examine, for the different important types, the percentage of all 
forties in each type with 1, 2, 3, 4, and more seed trees 18 and 20 
inches per acre, as already described. This is because 6 or 8 seed 
trees per acre on one forty are of no avail on another forty with 
but 1 or 2 seed trees. 
