PREPARATION OF YIELD TABLES. 101 



selected, and these are periodically measured, and the mean 

 taken. In this way yield tables will ultimately be obtained. 

 It is necessary to take several plots for each quality and age 

 gradation, so as to obtain average results, and because one or 

 other may become unfit for the purpose, in consequence of 

 unforeseen events. 



c. Measurement of a large number of Woods of different ages once, so 

 that Yield Tables are obtained immediately. 



Until yield tables, prepared as indicated under b, become 

 available, others for immediate use are required. These are 

 obtained by measuring fully- stocked sample plots in a sufficient 

 number of woods, representing all ages with moderate intervals. 

 Out of the data thus obtained, steady curves and tables are 

 prepared. A separate set of woods are required for each 

 quality class, and the great difficulty consists in selecting for 

 each set localities of the same quality. For this purpose 

 various methods have been suggested. Most of these start 

 from an indicating wood, while one, specially elaborated by 

 Baur,* starts from a different principle ; it will be dealt with 

 in detail further on. 



i. SELECTION OF WOODS FOR EACH QUALITY CLASS BY MEANS OF AN 

 INDICATING WOOD. 



The method is based upon the fact that the older wood has 

 been evolved out of the younger, in other words that the older 

 wood had at one time the same volume as the younger. Hence 

 it should be possible, by analysing a number of sample trees, 

 to ascertain the volume, or its forming factors, as basal area, 

 height and form factor, which the trees of a mature wood 

 had at the several periods of its life. Guided by the data thus 

 obtained, woods are selected, the dominant trees of which show 

 the same dimensions as those of the mature trees at the same 

 age. Such woods are assumed to give a true representation 

 of what the now mature wood was at the same age. When a 



* Professor of Forestry at the University of Munich. 



