RESULTS OF CUTTING IX THE SIERRA FORESTS. 
13 
Table 9. — Periodic annual basal area growth in per cent, Stanislaus National 
Forest. 1910-1'J.iO. 
Diameter classes. 
Species. 
4 to 11 
inches. 
12 to 17 
inches. 
18 to 23 
inches. 
24 to 29 
inches. 
30 to 35 
inches. 
36 to 41 
inches. 
42 up. 
Total. 
White fir: 
50 
9.11 
34 
6.35 
273 
4.92 
53 
5. 53 
9 
3.63 
4 
3.03 
71 
2.74 
21 
2.75 
4 
3.90 
8 
2.51 
55 
1.61 
14 
1.66 
3 
.87 
4 
2.36 
44 
1.39 
6 
1.27 
1 
.98 
5 
1.25 
27 
1.37 
4 
1.23 
4 
.63 
8 
1.03 
19 
.69 
1 
.42 
1 
.33 
12 
.51 
14 
.38 
6 
.18 
72 
Per cent 
2.33 
Sugar pine: 
75 
1.06 
Yellow pine: 
Number 
503 
1.46 
Incense cedar: 
105 
Per cent 
1.30 
ACCELERATION OF GROWTH. 
It is to be expected that the degree to which growth is accelerated 
by cutting will depend upon the proportion of the stand removed, 
provided age, site, composition, and other factors remain compar- 
able. As stated previously, variations in these factors on the plots 
here considered have been so great as to mask this relation. There 
are, however, several other factors more clearly emphasized by the 
present data than degree of cutting, which must be given considera- 
tion if enhancement of the growth of reserved trees is to be secured. 
Study of several hundred increment cores has shown that indi- 
vidual trees of all species and all ages seldom fail to respond if the 
trees removed are near enough so that light and soil-moisture re- 
lations are materially improved for those that remain. If, prior to 
cutting, a given tree was already receiving all the light it could 
utilize, its response will depend upon the increase in available soil 
moisture. As a rule, no acceleration is observable unless trees are 
removed within 50 or 60 feet. If the stand is already quite open 
before cutting, and the current rate of growth be high, no response 
may be apparent. An example of this is shown in the Sequoia plot 
in Table 7. Expressions of acceleration of growth, based on per- 
centage ratios between the average rates before and after cutting, 
do not, of course, give the total effect of the thinning, which is in 
reality the difference between the actual rate and that which would 
have been maintained with advancing age had no cutting been made. 
This is shown in Table 10 by comparing the growth rates of trees 
left after a cutting with those in adjacent virgin timber, using only 
yellow pines as nearly as possible the same in size, crown form, domi- 
nant class, and other respects, during the same periods as indicated 
for trees from the Sierra National Forest. The figures represent 
the percentage ratios between the rates maintained during one 5-year 
period and the preceding one. The remarkable decrease in rate 
during the last period on the cut-over area may be due to the com- 
bined effects of rapidly invading bear clover and reproduction, and 
a series of four exceptionally dry seasons from 1917 to 1920. 
49263°— 23 3 
