SILVICULTURAL MANAGEMENT OF BLACK SPRUCE IN MINNESOTA 37 



in uncut stands, hence there are many even-aged stands ; (3) in swamps 

 it forms a stable type that is not commonly invaded or succeeded by 

 other trees, but on upland it gives way to the white spruce-balsam 

 fir-paper birch association in the absence of periodic forest fires; (4) 

 although the best growth is made in full sunlight, the species can 

 endure rather heavy shade, and thus stands tend to become uneven- 

 aged; and (5) growth, although slow, is well-sustained up to about 

 100 years on the best sites and 160 years on the poorest sites, not taking 

 into account the submerehantable nonproductive swamps. 



Thrifty Swamp Stands 

 application of partial cuttings 



The term "partial cutting" as used in this paper is not synonymous 

 with the selection system of silvicultural management. The selection 

 system presupposes a distribution of age classes within a single stand 

 such that equal volumes of wood can be removed at each successive cut. 

 Although the natural stands of black spruce in Minnesota usually have 

 even-aged overstories, they become more or less uneven aged and 

 quite commonly are two-storied in appearance as a result of later 

 seeding-in or layering. Rarely, however, do they have such a nicely 

 balanced series of age classes as called for under the selection system. 

 Hence, these partial cuttings should be regarded as preliminary steps 

 in converting wild, unimproved stands into managed stands with 

 better size and age-class distribution and improved thriftiness (fig. 

 23). 



Unless a wild stand is in unusually favorable condition, the first 

 cutting can do little more than take out the most decadent and un- 

 thrifty trees. To try to do more would reduce the growing stock 

 unduly and thus lower future yields. Many stands are seriously un- 

 derstocked and others have such a high proportion of overmature 

 trees that nothing can be done except to cut the overmature material 

 and wait until the growing stock has been built up. Sometimes this 

 means practically clear cutting, but at other times it may be possible 

 to save some younger, healthy merchantable trees that ordinarily 

 would be removed in an unregulated operation. 



It is a prerequisite of partial cutting that the proper trees be marked 

 for cutting in advance of the logging operation, in order to retain those 

 having best prospects for growth. The cost per cord of marking small 

 trees such as black spruce is a considerable expense, but by no means 

 prohibitive in view of the benefits derived. On the Superior National 

 Forest many thousands of cords of spruce have been marked at an 

 average cost of 10 cents per cord (19) . 



Fortunately, it is possible to recognize the vigor of black spruce trees 

 with a fair degree of accuracy on the basis of outward appearance as 

 shown by a test with 84 trees chosen at random (table 9) (Id). In 

 most instances the trees ranked as "progressive" grew best and "regres- 

 sives" the poorest. The good growth of the 10- and 11-inch d. b. h. 

 trees that were ranked as "stable" and "regressive" indicates that, 

 although these trees have grown well in the past, they are now showing 

 outward signs of decline in vigor. Accordingly they should be cut 



