METHODS OF CONSTRUCTING YIELD TABLES. 99 



i. Selection of "Woods for each QrALiTY Class by Means of an 

 iNDicATiNfj 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 the factors from which it is calcu- 

 lated, namely, basal area, height and form factor, which the 

 trees of a mature wood had at the several periods of their life. 

 Guided by the data thus obtained, woods are selected; the 

 dominant trees of which show the same dimensions as those, 

 which the mature trees had at the same age. Such woods are 

 assumed to give true representations of what the now mature 

 wood was at the same ages. When a sufficient number of 

 woods of various ages has been selected, sample plots with 

 normal stocking are measured in them, and the data worked 

 up into a yield table for the corresponding quality class. 

 The same procedure is followed for all other quality classes. 



Various authors have gradually elaborated this system, first 

 Seutter as early as 1799, then Hossfeld in 1823. Huber, in 

 1847, was the first to give a regular method of working with 

 an indicating wood. He calculated the mean tree of a normal, 

 mature wood, analysed it and searched for younger normal 

 woods, the mean trees of which possess the same dimensions 

 as the mean tree of the mature wood had at the same ages. 

 His method is, however, wrong, because the mean tree of 

 the mature wood was not the mean tree at all former stages 

 of life. 



Theodor Hartig, and afterwards Eobert Hartig, analysed 

 the largest trees of the mature wood, and then searched for 

 younger woods, an equal number of the largest trees of which 

 show the same dimensions as the largest trees of the mature 

 wood had at the same ages. Such woods are considered as 

 having been produced on localities of the same quality, so that 

 they can be used for the preparation of one yield table. 



