34 BULLETIN 154, U. S. DEPARTMENT OF AGRICULTURE. 
TABLE 10.—Effect of thinning on yield per acre of lodgepole pine in individual 
sample plots on the Deerlodge National Forest, Mont. 
PLOTS SHOWING NO INCREASE IN RATE OF GROWTH. 
> 
Stand 20 years ago. see 
Periodic annual |Increase 
P e Se ey er 20] or de- 
if rio a ss years) oftrees | crease 
ae since Trees. Volume. an Verses left. in rate 
thinning thin- ; of 
in years. | M28 | Browah 
3 in after 
lyears.| Before | After | thin- 
" | Total.) Cut. | Left. | Total. | Cut. Left. Cut. Left. | thin- | thin- ning 
| ning. | ning. 5 
| eee | : | 
| Num-| Num-| Num- Per 
ber. ber. ber. | Cu.ft.| Cu.ft. | Cu.ft. | Inches. | Inches.| Cu.ft.| Cu.ft.| cent. 
AS se | “18 |- 850 290 260 1,955 521 1, 484 4.3 6.1 45.5 15.6 —66 
7h ete ne | 18] 430 320 110 2,336 1,486 850 5.9 6.7 27.0 19.8 —27 
10622 -2.- | 14 | 1,600 | 1,200 400 | 6,136 3,396 | 2,740 4.5 6.2 34.0 Ded —19 
10862222 | 20; 690 290 400 | 3,339 1,594 1, 755 6.0 6.1 a 0 4.7 —73 
Ips eee | 20 | 1,730] 1,120 610 2, 267 1,028 1, 239 3.2 4.3 1 8.1 —33 
PLOTS SHOWING INCREASE IN RATE OF GROWTH. 
CU Leeee 20 570 | 280} 290 | 951 399 552 4.2 4.1 16.1 22.6 40 
ee 15 650 420} 230] 1,305 697 608 4.2 4.4 21.6 30.4 40 
4552 = 15 910 500 410 | 1,434 563 871 3.5 4.2 31.8 36.3 14 
9535255: 14 930 730 | 200; 3,146] 2,316 830 4.9 5.3 6.2 17.5 182 
99025.< "52 20 | 1,050 500 550 | 2,049 985 1,064 4.3 3.7 15.0 Boe 121 
Obi === es 940 610 330 2,412 1,058 1,354 4.1 5.2 SB Ry 24.7 80 
100:22 2 = | 25 980 77 210 | 2,454 1, 430 1,024 4.1 5.6 8.2 21°53 160 
18 ht eee 20 580 | 470 110 2,216 1, 335 881 5.5 6.5 10.1 15.1 50 
2a ese 20 | 1,030 | 680 300 | 2,921 1,600 1,321 4.4 4.9 14.3 19.1 34 
dO (eta 20 520 270 250 3,443 1,388 | 2,055 5.7 6.7 15.9 21.4 35 
1 Yb Ee ee 13 840 490 300 | 5,178 2,887 | 2,291 6.0 5.9 15.9 28.8 81 
j bog the pe 24 440 176 264 | 4,459 2,286 | 2,173 8.9 6.9 9.5 29.2 207 
1h\: eee 24 585 485 100 | 3,769} 2,609 1,160 6.1 8.1 5.5 10.5 91 
Of the 18 plots measured, 13, or 72 per cent, showed an increase in 
the rate of growth after the thinning. In other words, the small 
number of trees left after thinning produced more cubic feet of wood 
per acre than would have been produced by the entire stand had it 
been left unthinned and continued to grow at the same rate as before 
the thinning. This result is particularly remarkable when it is re- 
membered that all of the plots had reached an age when the periodic 
rate of growth would ordinarily be decreasing. Table 9 shows that 
in normally stocked stands the periodic rate of growth in cubic feet 
increases rapidly up to 50 years, after which it decreases slowly. 
For this reason the falling off in the growth of the 106 and 123 year 
old plots is no greater than would be the case in unthinned stands of 
the same age, and very likely it is even less. ‘he apparently abnor- 
mal rate of decrease in the rate of growth of the 48 and 49 year old 
plots is probably due to the fact that they were nearly normal at the 
time of cutting, as indicated by their volume, with the result that the 
rather heavy thining had an injurious effect upon the trees left. The 
108-year-old plot is the only one for which the marked decrease in 
rate of growth can not be satisfactorily explained. 
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