6 
BULLETIN 1176, IT. S. 
DEPARTMENT OF AGRICULTURE. 
An expression of growth on an age basis is shown in Table 4, 
which gives average results from eight plots on the Plumas National 
Forest. These plots represent Site II, but a heavy stand and light 
cutting resulted in rather slow growth. 
Table 4. — Site II — Relation of age to annual growth, per cent, in basal area. 
(Eight plots, Massack, Plumas National Forest, curved.) 
50 
100 
150 
200 
250 
300 
350 
400 
Num- 
ber 
of 
trees. 
SPECIES. 
White fir 
4.50 
3.30 
2.40 
2.40 
2.20 
1.90 
1.40 
1.50 
1.25 
1.50 
.95 
.90 
1.10 
1.20 
.70 
.65 
0.90 
.80 
.60 
.55 
0.80 
.50 
.55 
50 
0.70 
.40 
.50 
.45 
0.60 
.40 
.45 
.40 
789 
437 
724 
1,249 
After 200 years, which roughly corresponds to the 24 to 29 inch 
size class, the rate of growth for all species under these conditions 
falls below 1 per cent annually. Probably 150 years, which corre- 
sponds to the 18 to 23 inch size class, should be the limit in cutting 
for all but sugar pine, in which value increment as well as better 
sustained growth has an influence, taking into consideration, of 
course, site and other factors. 
On some of the earlier sales many large, obviously mature pines 
were left, primarily to increase the proportion of pine reproduction, 
and their presence results in a material decrease in the average rate 
of growth maintained. Such trees represent a high risk of loss by 
fire or insects and, as will be seen later, have resulted in very little 
reproduction. How far leaving such trees is justified on the ground 
of improved quality of second cut will be discussed below. 
In selecting trees to be reserved it is of the greatest importance 
that the marker be able to estimate accurately degree of maturity, 
vigor, and probable effect of cutting, as well as soundness and seed- 
producing capacity, in order to utilize completely the potentialities 
of species and sites. Results may be neutralized by accidental losses 
or unproductive trees. Certain external features have been found 
most reliable as reflecting vigor, such as color and texture of bark, 
form of top, color and density of foliage, size of crown, and freedom 
from disease. 
CROWN SIZE AND FORM. 
The crown furnishes the most reliable index of what may be ex- 
pected from reserved trees. A dense, rich green, pointed crown 
gives certain evidence of a thrifty tree. The most significant single 
factors are crown length and form of top. If yellow pine is again 
used for demonstration, considering only trees between 12 and 30 
inches, on the basis of ratio of crown length to total height, the 
following relation, shown in Table 5, expressed in annual basal area 
growth, per cent, is found : 
