952 



A NATIONAL PLAN FOR AMERICAN FORESTRY 



TABLE 17. Number of trees, volume, and growth in typical stand second-growth, 

 river bottom hardwoods in lower Mississippi Valley Continued 



1 Only growth on sound trees has been calculated, but loss from mortality has not been deducted. 



2 Defective and suppressed trees not included in total effective growing stock. 



Because of past cutting and considerable burning these stands in- 

 clude a volume of defective material sufficient to displace at least one 

 third of the production that could be obtained if the growing stock 

 were all of vigorous and well-formed trees. The problem of removing 

 this material is difficult. Some of it, although unadapted to lumber 

 use, can be cut into small-dimension material for furniture manu- 

 facture, stave bolts, railroad ties, or other uses. It may prove possible 

 to remove from the stand by girdling large defective trees having no 

 prospective value. 



DETERMINATION OF GUIDING DIAMETER LIMITS FOR CUTTING 



In the division of this section entitled, " Application of the Selective 

 Cutting System," general principles on which trees should be selected 

 for cutting were discussed in some detail. Some of the data used were 

 drawn from the South. Figure 17, which bears on this subject as re- 

 lated to southern pines, is inserted here to show the relationship 

 between cubic volume and board measure for trees of different sizes. 

 It shows that trees 15 inches or more in diameter at breast height 

 average about 185 cubic feet per 1,000 board feet. Trees from 8 to 14 

 inches in diameter contain about 250 cubic feet per 1,000 board feet. 

 Disadvantages of producing lumber from southern pines less than 16 

 inches in diameter are as follows : 



1. As much as 60 percent more volume must be grown to produce 

 1,000 board feet. 



2. All this extra weight is expensive to handle. Partly for this 

 reason, logging and milling costs are higher for these sizes. 



