QUALITY OF WOODS. 269> 



sents the quality, the best way is to ascertain the volume of 

 the growing stock and the number of years in which it has 

 been produced. In dividing the volume by the age of the 

 wood, the mean annual increment is obtained. Both volume 

 and mean annual increment depend on the locality and the 

 past treatment of the wood. 



It is evident that in reality a multitude of different qualities 

 exist, but for practical work they are grouped into a few, 

 generally not more than five quality classes, which are 

 numbered I. to V. Of these I. should represent the lowest 

 and V. the best quality, but unfortunately the reverse num- 

 bering has been largely introduced. A still more convenient 

 way is to represent the best quality by 1 and the others in 

 decimals of 1. Each of these quality classes represents a 

 distinct yield capacity, which diifers with the species and 

 method of treatment. 



The quality can be determined with the help of yield tables,, 

 or the final mean annual increment. 



I. Determination of the Quality with the help of Yield Talks. 



The preparation of yield tables has been explained in Forest 

 Mensuration (page 96). Such tables represent the progress 

 of increment, or volume, throughout life for each quality class ; 

 hence, assessing the quality means, in this case, the selection 

 of the proper yield table. The difficulty is that for every 

 species and sylvicultural system a different set of yield tables 

 is required. It may even be desirable to have different sets. 

 for different localities, so-called local yield tables ; but such a 

 procedure is likely to lead to confusion, as different standards 

 of the quality classes are introduced into the account. Hence, 

 general yield tables are to be preferred, even if the same degree 

 of accuracy is not obtained as in the case of local tables. The 

 difference is, however, not considerable, as experience has shown 

 that, within reasonable limits, general tables give sufficiently 

 accurate data for the preparation of working plans. 



It has, for instance, been proved that the general yield tables 



