14 
BULLETIN 1176, U. S. DEPARTMENT OF AGRICULTURE. 
Table 10. — Comparison of basal area growth per cent on virgin and cut-over 
areas during successive 5-year periods, Sierra National Forest. 
Condition of area. 
Number 
of trees. 
Per cent of increase or decrease over 
preceding period for periods ending— 
1905 
1910 1915 
192% 
13 
28 
-3.1 
-3.7 
-12.7 
+ 57.8 
-8.5 
+ 42.0 
— 13.5 
Cut over 1906 
-58.6 
The ability to respond to the stimulus of cutting varies with the 
species. It has been stated that the amount of acceleration is in- 
versely proportional to the light requirements of the species. If this 
be true, we might expect white fir, one of our most tolerant species, 
to show a greater relative response than yellow pine, the least tolerant, 
in this region. The results obtained from increment borings are not 
in accordance with this expectation. It is difficult to get strictly com- 
parable conditions, and present data are not considered final. To 
obtain as nearly as possible comparable data for the two species, how- 
ever, there have been selected from many trees bored on each plot a 
few as nearly as possible similar in size at time of cutting, character of 
crown, and position. All the trees were dominants or codominants 
with large pointed crowns about which some cutting was done within 
a radius of 60 feet. Trees which stood in stream beds or were other- 
wise exceptional have been omitted. This limiting of the data gives 
the appearance of a scanty basis, but it is considered preferable to aver- 
aging together a larger number of trees which would introduce varia- 
tions, the effects of which could not be determined. The results are 
given in Table 11. 
Table 11. — Relative response of yellow pine and white fir. 
Yellow pine. 
White fir. 
Plot. 
Num- 
ber of 
trees. 
Aver- 
age di- 
ameter 
breast 
high. 
Annual basal 
area growth. 
Accel- 
eration. 
Num- 
ber of 
trees. 
Aver- 
age di- 
Annual basal 
area growth. 
Accel- 
Before. 
After. 
breast 
high. 
Before. 
After. 
eration. 
20 
25 
32 
31 
13 
7 
20.6 
18.9 
18.1 
20.0 
15.8 
18.5 
P.ct. 
0.53 
1.15 
1.15 
1.73 
1.93 
1.70 
P.ct. 
0.83 
1.46 
1.34 
1.87 
3.19 
3.48 
P.ct. 
+56.6 
27.0 
16.5 
8.1 
65.3 
104.7 
9 
11 
6 
11 
8 
8 
12.7 
17.4 
11.4 
18.1 
15.8 
12.3 
P.ct. 
1.39 
3.67 
2.09 
3.65 
2.25 
5.53 
P.ct. 
1.48 
4.20 
2.48 
3.87 
4.26 
7.31 
P.ct. 
+6.5 
Tahoe 
14.4 
18.7 
Stanislaus-2 
6.0 
Sierra 
89.3 
Stanislaus-1 
32.2 
In every case white fir has grown at a much higher rate than yel- 
low pine, but the relative increase after cutting was greater in only 
two of the six cases. 
With increasing age the percentage of acceleration, as well as the 
absolute rate attained after cutting, decreases. 
Suppressed trees growing at a slow rate show relatively greater 
response to cutting than those which were always dominant, al- 
though the rate attained may be much less. 
