34 



BULLETIN 154, U. S. DEPARTMENT OF AGEICULTUBE. 



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. 





Pe- 

 riod 



since 

 thin- 

 ning 



in 

 years. 



Stand 20 years ago. 



Periodic annual 

 growth (for 20 

 years) of trees 

 left. 



Increase 



Age at 

 time of 

 thinning 



Trees. 



Volume. 



Average 

 diameter. 



crease 

 in rate 



of 

 growth 

 after 

 thin- 

 ning. 



m years. 



Total. 



Cut. 



Left. 



Total. 



Cut. 



Left. 



Cut. 



Left. 



Before 

 thin- 

 ning. 



After 

 thin- 

 ning. 



48 



49 

 106 



108 



123 



18 

 18 

 14 

 20 

 20 



Num- 

 ber. 

 550 

 430 



1,600 

 690 



1,730 



Num- 

 ber. 

 290 

 320 



1,200 

 290 



1,120 



Num- 

 ber. 

 260 

 110 

 400 

 400 

 610 



Cu.ft. 

 1,955 

 2, 336 

 6,136 

 3,339 

 2,267 



Cu.ft. 

 521 

 1,486 

 3,396 

 1,594 

 1,028 



Cu.ft. 

 1,434 

 850 

 2,740 

 1,755 

 1,239 



Inches. 

 4.3 

 5.9 

 4.5 

 6.0 

 3.2 



Inches. Cu.ft. 



6.1 45.5 

 6.7 27.0 



6.2 34.0 

 6.1 17.2 



4.3 12.1 



Cu.ft. 

 15.6 

 19.8 

 27.7 



4.7 

 8.1 



Per 



cent. 

 -66 

 -27 

 -19 

 -73 

 -33 



PLOTS SHOWING INCREASE IN RATE OF GROWTH. 



44 

 44 

 45 

 95 

 95 

 95 

 100 

 119 

 125 

 127 

 141 

 151 

 154 



20 



570 



280 



290 



951 



399 



552 



4.2 



4.1 



16.1 



22.6 



15 



650 



420 



230 



1,305 



697 



608 



4.2 



4.4 



21.6 



30.4 



15 



910 



500 



410 



1,434 



563 



871 



3.5 



4.2 



31.8 



36.3 



14 



930 



730 



200 



3,146 



2,316 



830 



4.9 



5.3 



6.2 



17.5 



20 



1, 050 



500 



550 



2,049 



985 



1,064 



4.3 



3.7 



15.0 



33.1 



25 



940 



610 



330 



2,412 



1,058 



1,354 



4.1 



5.2 



13.7 



24.7 



25 



980 



770 



210 



2,454 



1,430 



1,024 



4.1 



5.6 



8.2 



21.3 



20 



580 



470 



110 



2,216 



1,335 



881 



5.5 



6.5 



10.1 



15.1 



20 



1,030 



680 



350 



2,921 



1,600 



1,321 



4.4 



4.9 



14.3 



19.1 



20 



520 



270 



250 



3,443 



1,388 



2,055 



5.7 



6.7 



15.9 



21.4 



13 



840 



490 



350 



5,178 



2,887 



2,291 



6.0 



5.9 



15.9 



28.8 



24 



440 



176 



264 



4,459 



2,286 



2,173 



8.9 



6.9 



9.5 



29.2 



24 



585 



485 



100 



3,769 



2,609 



1,160 



6.1 



8.1 



0.0 



10.5 



40 

 40 

 14 



182 



121 

 80 



160 

 50 

 34 

 35 

 81 



207 

 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. Ine 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. 



