SILVICULTURAL MANAGEMENT OF BLACK SPRUCE IN MINNESOTA 11 



is much more gradual. For example, on three plots taken at intervals 

 of about 300 feet in a 140-year-old stand in Koochiching County, 

 dominant trees were found to have average heights of 68 feet, 52 feet, 

 and 24 feet. 



Changes in productivity of site from place to place within a swamp 

 usually can be associated with some discernible physiographic condi- 

 tion such as depth of peat, or drainage, but no satisfactory method 

 has been worked out for accurate determination of the productivity 

 of swamps except by measurement of the trees. Merchantable 

 stands u most often are found on peat less than 2y 2 feet in thickness, 

 less often on peat 2% to 5 feet in thickness, and occasionally where 

 the peat is 18 or 20 feet deep. Some attention was* given to the pos- 

 sibility of finding associated plants that would serve as indicators of 

 site quality but none were detected. 



The actual average volume of pulpwood per acre found over any 

 considerable area is small, due to the inclusion in the statistical com- 

 pilations of many poorly stocked and comparatively low site swamps. 

 For example, in the Rainy River district, the average volume per acre 

 in the 3- to 9-inch or "cordwood" size-class in 1934 was as follows : 



» 



Species : Cords 1 



Black Spruce 7. 6 



Tamarack . 8 



Northern white-cedar _ . 7 



Others 2 . 



9. 



1 Volume in trees 5.0 inches d. b. h. and over to a 4-inch top diameter inside 

 bark. 



2 Chiefly balsam fir, paper birch, and quaking aspen. 



Well-stocked stands of cordwood size, of course, contain much larger 

 volumes than the average given above — up to about 35 cords per acre. 



UPLANDS 



Black spruce occurs to some extent in practically all upland forest 

 types in northern Minnesota, but generally is of little importance 

 except in the mixed forests classed as spruce-fir type. For the State 

 as a whole, black spruce constitutes about 7 percent of the volume in 

 trees 5 inches and larger d. b. h. in the spruce-nr type. In northeastern 

 Minnesota there are occasional nearly pure stands of black spruce on 

 the rock outcrop formations of the Laurentian Shield and the species 

 often is present in considerable numbers in the jack pine type (fig. 9) . 

 For example, on the Kawishiwi Experimental Forest near Ely, Minn., 

 6 percent of the area was classed as upland black spruce type. Eight 

 percent of the merchantable volume in jack pine types on the experi- 

 mental forest was black spruce. 



When black spruce is found growing in mixed forests, it usually is 

 smaller in size than its associates, such as paper birch, quaking aspen, 

 and jack pine. However, the principal components of these stands, 

 including the black spruce, are even-aged. 



11 Under current logging practices in Minnesota, spruce pulpwood seldom, is 

 cut unless at least 4 or 5 cords per acre can be taken mainly from trees that will 

 yield two or more 100-inch bolts to a top diameter of 3 inches inside bark. 



