SILVICULTURAL MANAGEMENT OF BLACK SPRUCE IN MINNESOTA 45 



basal area or one-third of the volume of trees over 5 inches d. b. h. will 

 result in the largest net gains in volume. The reasons are simple : 



1. By leaving many trees, a large volume of wood can be produced even though 

 the individual trees do not grow rapidly. 



2. Light cuttings give an opportunity to take out the more decadent trees and 

 leave the vigorous ones ; hence, the natural mortality losses should be considerably 

 curtailed. 



A clue to the possibilities for recovering additional volume by fre- 

 quent light cuts is indicated by the extent of mortality in undisturbed 

 stands. A 40-year-old fully stocked stand on medium site contains 

 3.675 trees per acre but a stand on the same quality of site contains only 

 1 ,277 trees per acre when 120 years old (table 8 ) . In other words, two- 

 thirds of the trees die during this 80-year period. This is a great 

 waste of wood. Obviously, many of these trees die long before they 

 attain merchantable size, but some of them reach merchantable size 

 first and some of the more promising ones could be saved for further 

 growth by the harvesting of over-topping decadent or unthrifty trees. 



Existing standards of utilization have considerable effect in deter- 

 mining the extent to which small unthrifty trees can be salvaged. At 

 present few pulpwood buyers accept bolts smaller than 3 inches inside 

 bark at the small end and some in Minnesota hold to a 4-inch top. In 

 a utilization study conducted near Big Falls, Minn., it was found that 

 where both large and small trees were removed, the gain in volume 

 when tops were utilized down to V/ 2 inches instead of the usual 3% 

 inches amounted to 22 percent (1) . In a later study 26 the cord volume 

 increase for 2% -inch utilization was 27 percent and for 3-inch utili- 

 zation 21 percent, compared with 4-inch top cutting. About 10 per- 

 cent of this increase came from small trees between 4 and 5 inches 

 d. b. h., and the remainder from the additional usable sticks per tree. 

 Bolts smaller than 3 inches in diameter have, in the past, been con- 

 sidered by some mills to be more difficult to bark than standard pulp- 

 wood. It was concluded, however, following a recent mill test -' that 

 there is no loss in the barkers of sticks down to 2i/2-inch top diameter, 

 and the average barking time is not excessive for spruce which is not 

 frozen. Even without barking, small bolts can be used for certain 

 products, such as insulating material. There is, of course, less solid 

 wood in a stacked cord of small wood. However, the main objection 

 to small wood is the greater cost of handling the greater number of 

 sticks per cord. Nevertheless, the trend is toward closer utilization 

 practices. As a result, the quantities of wood to be recovered and the 

 amount of stand improvement that can be accomplished in partial 

 cuttings will be considerably increased. 



STRIP CUTTING 



Considerable interest has been aroused and some experimentation 

 has been done in strip cutting, that is, clear cutting in alternate strips. 

 Perhaps its chief appeal lies in the ease of administration. The 



26 Z as ada, Z. A., Hubbard, John W., and Adams, Earl J. a study to deter- 

 mine THE VARIATION IN VOLUME AND COSTS OF BLACK SPRUCE CUT TO DIFFERENT TOP 



diameters. Lake States Forest Expt. Sta., Minn. Forest Service, and Minnesota 

 and Ontario Paper Company. 33 pp. 1947. [Mimeographed.] (Revised Feb. 

 27, 1948.) 



