584 JOURNAL OF FORESTRY 



To illustrate the calculation of the normal stock three examples are 

 given, two for the selection system and one for the group system. As 

 stated above, Heyer's formula is used. Periodic revisions at ten-year 

 intervals are recommended with local determinations of the actual in- 

 crement. For the latter purpose sample plots carefully marked to 

 insure accurate remeasurement may be used. Every revision of the plan 

 brings more accurate results. A long transition period is recommended 

 when the stock is abnormal rather than abrupt decreases or increases of 

 the annual budget. The calculations which determine the normal stock 

 are relatively easy with a clear-cutting system, but much more compli- 

 cated with selection stands. For the latter, division of the stand into 

 three equal age classes should give the following relations : 



Per cent of area 



Youngest age classes 17 



Middle age classes 48 



Oldest age classes 35 



It is obvious that the relation between normal stock and normal yield 

 will vary with the length of the rotation and the species. The longer 

 the rotation and the slower growing the species the smaller the per cent 

 of the normal stock which the annual felling budget represents. For 

 example, with fir on average sites the per cent varies from 5.39 for a 

 60-year rotation to 1.77 for a 120-year rotation. Likewise a 60-year 

 rotation ranges from 5.39 for fir to 3.04 per cent for pine in Saxony. 



For clear-cuiting systems the calculation of the annual budget is 

 relatively easy. Mantel's formula is the simplest for this purpose, 

 especially since it does not require a knowledge of the length of 

 rotation. But with selection forests the process is more complicated. 

 The author recommends the following procedure. 



1. Determine a diameter limit which will insure the removal of only 

 mature trees. 



2. Caliper all trees over this diameter limit and calculate their vol- 

 ume. This actual yield should be compared graphically with the ideal 

 yield as given by normal yield tables. 



3. Revise the yield at least every ten years. This system has the 

 advantage of conservatism but the frequent revisions prevent deficits 

 or the accumulation of surpluses. Furthermore, and important points 

 in mountain selection forests, the calipering is reduced to a minimum 

 and there are no stem analyses or increment borings to take and figure 

 out. B. E. F. 



K. W. W. 



Aus- dem Gebietc unserer Porsic'mrichtung. Schweizerische Zeitschrift fiir 

 Forstwesen, March, April/May, June/July, August/September, October/Novem- 

 ber, December, 1918, pp. 49-55; 79-98; 120-136; 162-76; 195-21 1; 235-43. 



