Periodical Literature 261 



methods. Nevertheless it is essential to determine for each stand 

 whether the actual growing stock should be increased or dimin- 

 ished.^ In practice one can best judge of the normal growing 

 stock by comparison with the actual on the basis of the con- 

 dition of the stand and by comparison with other stands similarly 

 situated. 



Unfortunately, age of the trees does not furnish a basis of 

 regulation in selection forest. Trees of the same diameter vary 

 greatly in age. All attempts to use average age bring artificial 

 results. In selection forest one must get along also without a 

 definite rotation age. The condition of the individual tree gov- 

 erns its time of cutting. 



Since uniform age classes are lacking, that is, since individual 

 stands do not belong to a definite age class one does not need a 

 yield table in the usual sense. The ordinary yield table bases on 

 age of stands. But what can be used in place of age in a yield 

 table for selection forest? Only empirical tables which give the 

 estimate of certain selection stands and show the size classes, the 

 growing stock, the current annual increment and the actual volume 

 secured in cutting. 



Since the average age of a well regulated selection forest 

 remains practically the same, it stands to reason that the current 

 annual increment and the mean annual increment are the same. 

 Two ways are possible of determining the current annual 

 increment. 



1. By periodic remeasurement of the stand with identical 

 methods. (For example see F. Q. XIII, pp. 60-63.) 



2. By measurement of sample trees as average of the stand. 

 The former method is that of the Methode du Controle and 



depends for its accuracy upon the accuracy of measurement. The 

 latter is too well known to require comment. 



The determination of cut in selection forest must depend on 

 volume alone, that is, on the growing stock and the increment 

 which have been determined separately and hence check each 

 other. Such methods are : 



1. Divide the volume of the oldest size classes by the annual 

 increment of the entire stand. This will give the number of years 



' The author of the Methode du Contr61e has empirically determined an 

 average growing stock of 350 cubic metres per hectar (5,000 cubic feet per 

 acre). See F. Q., XIII, pp. 43-46. 



