910 A NATIONAL PLAN FOR AMERICAN FORESTRY 



The sum of the values tied up in diameter classes at the left of and 

 above the heavy line constitutes the investment in growing stock in 

 terms of immediate realization value. All smaller tree sizes that show 

 no immediate realization value can be valued, if at all, only by dis- 

 counting the value they will have when merchantable. 



The rate of earnings made by the trees in the residual stand is the 

 principal guide in choosing trees for cutting. Where the forest is 

 very deficient in growing stock it may be desirable to raise the guiding 

 limit. If, on the other hand, there is a surplus-of growing stock, more 

 small trees should be taken, to increase the growth and earnings of 

 those left. At all times, trees of less than the chosen size but defective 

 or indicated for removal to thin the stand should be taken if they can 

 be marketed without loss. Selecting high-value saw timber and other 

 valuable trees to produce the main income, and surplus, and ill-formed 

 trees for cordwood uses, not only provides the forest owner with the 

 maximum income from his property but also provides cord wood- 

 using industries with cheaper products than can be produced inde- 

 pendently of saw timber. 



Conditions in typical stands in most of our important forest types 

 are shown in 15 figures and 12 tables in conjunction with descriptive 

 text distributed throughout the following regional discussions. In 

 most of these figures heavy curved lines indicate the suggested limits 

 of the permanent growing stock. ^ It should be emphasized that while 

 the suggested growing stock will without doubt provide for satis- 

 factory rates of production in practically every case, these conclusions 

 are only tentative. Careful investigation is needed to fix growing 

 stock limits in any given case, and even then adjustments will con- 

 stantly be necessary. These adjustments should be based on the 

 fundamental principle of retaining a growing-stock investment 

 sufficient to make the earnings of a forest property approximate the 

 maximum possibilities. In the final analysis maintaining a sufficient 

 growing stock is a matter of thrift saving sufficient of the forest 

 capital to provide for a high rate of continued forest productivity. 



f The reasons for the distribution of cubic volume among the different 

 diameter classes and timber groups are as follows : The small timber 

 (8- to 12-inch diameter classes) should be maintained only in sufficient 

 numbers and volume to replace losses by mortality in all groups and 

 recruit the medium timber as trees are removed from it by cutting 

 or growth into the large timber group. The medium timber group 

 (14- to 20-inch diameter classes), since it is generally the source of the 

 highest investment earnings, should usually be maintained at a 

 maximum of volume. Exceptions to this occur in the Pacific coast 

 region where the production of large timber should be a constant aim. 

 In other regions the proportion of the stand composed by the large 

 timber group (22 inches diameter and over) may be expected to fall 

 off rather rapidly with increase in size of the trees, because the trees 

 have passed the point of large investment earnings. In these regions 

 only a few exceptionally well-formed and vigorous trees should be 

 held until they grow into the large-diameter classes. 



