32 
BULLETIN 1291, IT. S. DEPARTMENT OF AGRICULTURE 
The results, reduced for the sake of simplicity to a common basis 
of 100 as the volume of the original stand on each plot, are shown 
in Table 20. 
Table 20.— Effect of 
thinning aspen. 
(Percentage of original volume.) 
Grade thinning 
Original 
average 
diameter 
breast 
high 
Cut 
Left 
Died 
5 years 
Remain- 
ing after 
5 years 
Total 
yield 
green 
Tota 
yield, 
includ- 
ing dead 
A 
Inches 
3.01 
3.24 
3.06 
3.80 
4.52 
5.10 
3.07 
2.91 
4.23 
5.10 
5.72 
5.90 
4.50 
5.10 
3.73 
3.43 
Per cent 
12 

10 

12 

21 

19 

21 

24 

23 

17 

13 

Per cent 
88 
100 
90 
100 
88 
100 
79 
100 
81 
100 
79 
100 
76 
100 
77 
100 
83 
100 
87 
100 
Per cent 

3 
1 
8 
2 
6 
1 
15 

6 
1 
5 
2 
6 
2 
14 
1 
8 
6 
7 
Per cent 
106 
117 
103 
103 
92 
102 
89 
97 
91 
102 
86 
105 
79 
102 
96 
99 
93 
103 
93 
103 
Per cent 
118 
117 
113 
103 
104 
102 
110 
97 
110 
102 
107 
105 
103 
102 
119 
99 
110 
103 
106 
103 
Per cent 
118 
120 
A. ■_ 
114 
None . ._ .- . 
111 
A 1 
106 
None 2 
108 
B 
111 
112 
B 
110 
108 
C___ 
108 
None. 
110 
C , 
105 
108 
c 
121 
113 
Average: 
Thinned 
111 
111 
Cleaned. . _ - 
2.96 
2. 56 
112 
110 
Plate IX, Figure 1. 
2 See Plate IX, Figure 2. 
The net result of thinning is to get the aspen in a green state 
rather than dead, which is not worth the labor expended in thin- 
nings; for material this size is no more valuable green than dead, 
being generally unmerchantable in either case. Only four plots out 
of the nine show a larger total yield on the thinned plot. No analysis 
of conditions of site, age, or degree of cutting explains the matter, 
which seems to be mere chance. The figures show very plainly the 
slowness of net growth in aspen at ages of 40 to 80 years. Compe- 
tition is very strong at that time, and in two- cases an actual reduc- 
tion in volume in the 5-} T ear period is shown on account of heavy 
mortality in the suppressed class. On the average, an increase of 
only 3.3 per cent is shown in five years, or an annual increment of 
0.6 per cent, while the yield table indicates an increment percentage 
of about 1.5 at this age. The discrepancy is largely due to the 
fact that the yield table takes into account only the stand more than 
4 inches in diameter breast high, which is increasing rapidly at 
about that age on account of large accessions from below the 4-inch 
class. 
The reason why thinnings fail to show stimulated growth is that 
the stimulation is in the smaller-sized trees the volume of which is 
small, while the largest trees show little or no acceleration, or even 
reduced increment, after thinning. 
Aspen does not recover readily from suppression, as is shown by 
the loss by death in nearly all thinning plots during the 5-year 
period after treatment. In every case death was clearly the result 
of suppression before thinning, which reduced the vitality so 
markedly that even with much increased light after thinning death 
ensued. 
