SILVI CULTURAL MANAGEMENT OF BLACK SPRUCE IN MINNESOTA 39 



soon. The trees were judged as to vigor chiefly on the basis of the 

 following characteristics : 



1. Dead tip (upper 1- to 5-foot portion of crown). — This indicates a distinctly 

 unthrifty condition. 



2. Length and density of crown. — A long and dense crown is evidence of good 

 growth. Conversely thin foliage and numerous dead branches or a short crown 

 indicate poor growth. 



3. Appearance of bark. — Dark bark with small tightly attached scales is 

 characteristic of younger and more vigorous trees. Cracks in the bark to accom- 

 modate larger diameters are evidence of good growth. Gray, shaggy bark is a 

 distinguishing feature of trees over 100 to 125 years old. 



Several methods for reserving part of the trees without incurring 

 the expense and trouble of marking have been used on timber sales 

 on public lands. All of these methods are based on the principle of 

 leaving trees that are smaller than a stated size. The minimum sizes 

 specified may be related to d. b. h., stump diameter, or number of 

 merchantable pulpwood bolts. The stump diameter limit specifica- 

 tion has the advantage that the stumps provide tangible and easily 

 proved evidence of violations of cutting regulations. It also en- 

 courages the cutting of low stumps. On the other hand, the taper of 

 black spruce trees near the ground line is both rapid and variable, so 

 that it is difficult to set a limit that will give consistent results. 



Table 9. — Diameter growth rates of black spruce for the period 1931- 

 1940, by vigor and 1-inch d.b.h. classes 





D. b. h. class (inches) 



Average d. b. h. growth for 10 years 

 by vigor classes 





Progressive 



Stable 



Regressive 



4 



Inches 

 0. 71 

 1.02 



. 71 

 .68 



Inches 

 0. 58 

 . 63 

 .75 

 . 51 

 .54 

 . 59 



Inches 

 0. 24 



5 _ ___ 



. 22 



6 



. 20 



7 



. 29 



8 _________ 





9 



. 79 



. 25 



10 



. 80 



11 _. 





.74 







Average__ 











. 78 



. 62 



.33 



All the systems of minimum size designation — d. b. h., stump di- 

 ameter, and number of bolts — generally require close supervision of 

 the cutters and frequent inspection in order to get adherence to the 

 rules, because there is a widespread inclination to "chisel" on such 

 specifications. Sometimes, also, cooperatively inclined operators fail 

 to cut all of the trees that are permitted. For example, one farmer- 

 logger operating on State forest land, who was anxious to do a good 

 job, left 50 trees per acre that were above the minimum diameter 

 of 9 inches at the stump. It is evident that minimum size designation 

 requires extra supervision. However the chief objection to size desig- 

 nation is that at best it only approximates good marking, and fre- 



