44 



CIRCULAR 791, U. S. DEPARTMENT OF AGRICULTURE 



peared to have died chiefly as the result of long extended suppression. 

 In the heavily cut stands many small trees of seemingly good thrift 

 died for no obvious reason. Sudden exposure apparently has some 

 harmful effect. Probably insects, - mistletoe, disease organisms, 

 senility and mechanical injuries also contributed to the undiagnosed 

 causes of death. But, whatever the causes of mortality may have 

 been, the losses following light cutting were not sufficiently serious as 

 to make such cutting impracticable. 



GROWTH IN CUT-OVER STANDS 



In another phase of the analysis of response of black spruce to 

 various degrees of cutting, it was found that the total growth, not 

 taking into account mortality, was almost directly proportional to 

 the volume of timber left (table 10) (21). The most lightly cut plots 

 grew nearly one cord per acre per year for the 5-year period and the 

 most heavily cut plots about one-tenth cord per acre per year. The 

 fact that growth percents, before deducting mortality, were as high 

 in light cuttings as in heavy cuttings, is evidence that the trees left 

 in the light cuttings were wisely chosen for their vigor, in contrast to 

 the "choppers' choice" on the heavy cuttings where only small trees 

 were left. 



Table 10. — Volume growth per acre in black spruce stands during 

 5-year period following cutting 



Basal area cut 

 (percent) 



Volume 1 

 left after 

 cutting 



Gross annual 

 growth 



Net annual 

 growth 2 



25 



Cords 



20. 7 



14. 8 



12.4 



9. 2 



5. 5 



2.5 



1. 5 



Cords 

 0. 98 

 .72 

 .50 

 . 50 

 .28 

 . 10 

 .08 



Percent 

 4.7 

 4.9 

 4.0 

 5.4 

 5. 1 

 4.0 

 5.3 



Cords 



0. 88 



. 54 



.02 



.20 



.04 



-. 10 



-.06 



Percent 

 4. 3 



40 



3. 6 



49 _ __ 



. 2 



59 _ 



2. 2 



72 



. 7 



82 



— 4. 



89__ 



— 4. 







1 Volume of trees over 3.5 inches d. b. h. from a 1-foot stump to a 3-inch top 

 d. i. b. 



2 Growth after deducting mortality. No correction has been made for cull, but 

 this seldom exceeds 5 percent in spruce pulpwood timber. 



Net growth, after deducting mortality, ranged from almost nine- 

 tenths cord on the- lightest cuttings to negative values on cuttings 

 heavier than 72 percent by basal. area. It is unlikely that a growth 

 rate of nearly nine-tenths cord per acre per year can be maintained 

 indefinitely, but a considerably lower rate would still be satisfactory. 

 Definite proof of the growth rates that will result from periodic light 

 cuttings cannot be obtained until such successive cuttings have been 

 made, but it appears safe to predict that one-third to one-half more 

 wood can be recovered by this method than by clear cutting. The 

 study indicated that initial cuts which remove about 25 percent of the 



