68 
BULLETIN" 1402, U. S. DEPARTMENT OF AGEICULTUEE 
Response to cutting is more prompt, longer sustained, and greater 
on good than on poor sites. The increased percentage may be 100 
or more if the trees left are \yell selected and well spaced. 
The attainable growth on reserved trees for different qualities of 
soil is well illustrated in Table 6, which is based on data obtained 
from permanent sample plots. 
Table 6. 
-Percentage of average annual 'basal area growth of yellow pine for 
10 years after cutting^ 
Basic data 
Growth, by inch diameter 
classes 
Site 
National forest 
Number 
of trees 
12-17 
18-23 
24-29 
ni 
Shasta 
288 
261 
306 
160 
33 
76 
Per cent 
0.78 
1.35 
1.52 
2.69 
3.27 
4.72 
Per cent 
0.62 
.90 
.98 
1.61 
3.00 
4.21 
Per cent 
0.45 
III 
Tahoe - ...... 
.67 
II- 
Plumas 
.70 
11+ 
1.29 
I 
Sierra - _ . - 
.78 
I 
Sequoia 
2.75 
1 Basal area signifies cross-section area of trees at 4.5 feet from the ground. 
On the better sites a rate of growth of 3 to 4.75 per cent is ob- 
tained on trees up to 24 inches in diameter, whereas on trees from 
24 to 30 inches the rate falls to 2.75 per cent. On medium and poor 
sites the rate is still lower. These figures are conservative, since 
volume growth rate is always greater than basal area growth rate, 
on trees that are making height growth. Thrifty young trees of 
the type reserved under desirable forest practice would certainly 
exceed the rates above indicated. 
RELATIVE GROWTH RATE OF DIFFERENT SPECIES 
The same studies have also given an excellent basis for determin- 
ing the relative growth possibilities of the principal tree species. 
On medium sites, for trees 18 to 24 inches in diameter, the relations 
between annual basal area growth percentages are indicated in 
Table 7. 
Table 7. — Comparative grotvth rate of different species, medium sites 
Species 
White fir 
Sugar pine.-- 
Yellow pine-. 
Incense cedar 
Annual 
growth 
Per cent 
2.22 
2.07 
L50 
1.21 
Trees 
Number 
463 
81 
156 
321 
Considering rate of growth, sugar pine is a better tree to leave 
than yellow pine, and it also maintains a good rate of increment 
to a higher diameter than any other species. White fir, because of 
its high growth rate is, where sound, a desirable species to leave. 
Douglas fir appears to fall between yetlow and sugar pines, 
though this species has not been so thoroughly studied as the others. 
