40 BULLETIN 24, U. S. DEPARTMENT OF AGRICULTURE. 
area the stand had been opened up too severely, and toward the cen- 
ter many of the dominant trees appeared to have been taken along 
with the smaller ones. One half-acre plot was laid off, however, 
which there was a fairly even distribution of the remaining trees, 
and from which the smaller or medium-sized trees were the ones 
chiefly removed. It happened that this small area was properly 
thinned. Table 7 shows the condition in this half-acre plot in con- 
trast to the average for stands of this age. 
TABLE 7.—E£ ject of thinning on cottonwood stands. 
= Average 
Trees per 
Toial : diameter of 
numberof 2te over Average treesabove Stand per 
2 14inches | diameter 
trees per = 14 inches acre. 
SS diameter, ofall irees. ne 
’ ©- | breasthigh tsi ; 
| breasthigh 
Inches. Inches. Board feet 
AVCTATG DIGE oS eee ee eee 215 34 10.5 15.5 4,000 
Thinned plots: 2: fn52 0 ees 132 | - 50 12.3 15.9 | 7,500 
In the thinned plot there were approximately 40 per cent fewer 
trees per acre than in the average plot. Of trees over 14 inches in 
diameter, on the other hand, there were actually 47 per cent more, 
and the average diameter of all trees was 17 per cent larger in the 
thinned than in the average plot. 
The results in this one thinned stand are corroborated by measure- 
ments of five 15-year-old plots of cottonwood across the river from 
Helena, Ark., in which was an understory of sycamore and a few 
other species, all more tolerant than cottonwood, and of the same 
age as the latter though only one-third the height. It was therefore 
apparent that the cottonwood started in mixture with the sycamore, 
but being of more rapid growth soon overtopped it, thereby freeing 
itself from crowding and side shade. Thus, while not actually 
thinned, it had passed through a natural stage in some respects 
closely paralleling artifical thinning. Im these five plots the board- 
foot yield noticeably exceeds the average for the same age stands. 
TABLE S8—HEffect of associate species on form, growth, and yield of cottonwood. 
Number | Average 
Total of trees | | diameter 
peracre | Average trees over >: 
Age 15 years. pee! overli | diameter | 12inches » ae 
ae = inches j ofalltrees. diameter, = 
Pp - | diameter | breast- 
breasthigh. | - high. 
Inches. Inches. Board fee. 
Averace of all plots: 3. == == = ee 22 9.2 14.9 2,400 
275 
Average of 5 plots with sycamore under- | : 
SOLY= Se eee ee oe ee ee 200 27.6 | 10.4 15.1 3,040 
