A NATIONAL PLAN FOR AMERICAN FORESTRY 



923 



River region (18). On such areas it is recommended that the first 

 cutting take the diameter classes to the right of the broken lines on the 

 diagrams, which include all diameters above an average of about 44 

 inches. The reasons for this limit on cutting, brought out by an 

 intensive investigation during 1932 of results of logging on these areas, 

 are as follows : 



1. If logging is confined to these limits the net stumpage realized 

 in the Columbia River log market, even in the depression year of 1932, 



6 8 10 12 14 16 18 20 22 ZA 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 7^ 74 76 78 



6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 4E 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 

 DIAMETER BREAST HIGH (INCHES) 



EXISTING GROWING STOCK - HEMLOCK 



EXISTING GROWING STOCK SPRUCE 

 SUGGESTED LIMITS OF IMMEDIATE CUTTING 

 SUGGESTED LIMITS OF PERMANENT GROWING STOCK 



Timber groups totals omitted on graphs A and B in order to show distributio 

 of volume in higher diameter classes 



FIGURE 6. Distribution of cubic volume by diameter classes on average acre in two typical spruce-hemlock 

 stands, lower Columbia River region. A, Some spruce occurs in lower diameter classes: 5,550 cubic 

 feet of spruce, 5,120 cubic feet of hemlock per acre; B, All spruce is 56 inches or more in diameter: 

 2,970 cubic feet of spruce, 7,820 cubic feet of hemlock per acre. 



exceeds $6 per M board feet. The remaining diameter classes, con- 

 sisting mostly of hemlock, will net considerably less than $2 per M 

 board feet. Figure 7 shows the margin between log prices and logging 

 costs for the spruce and hemlock, respectively. 



2. In these old trees the otherwise merchantable portion of the bole 

 already averages 35 percent defective. The trees are losing much 

 more volume than the hemlock stand can grow ; in fact, the growth of 

 the hemlock is offset by the constant dropping out of hemlock trees 

 reaching the age limit. 



3. Cutting the spruce and some of the largest hemlock will give 

 the smaller-sized hemlock a chance to develop. This will prepare the 



