256 COLLECTION OF STATISTICS. 



real increment must be ascertained. When the yield is iixed 

 for only a limited period, the current increment must be 

 ascertained for that number of years, or the mean annual 

 increment of the past is substituted for it. 



For financial questions, the volume-, quality- and price- 

 increment must be determined, as well as the capital invested 

 in the forest, so as to calculate the indicating or forest per 

 cent. The latter is necessary only for Avoods, the financial 

 ripeness of which is doubtful, that is to say, for woods, which 

 are approaching the normal final age, and woods, which have 

 suft'ered by injurious agencies, such as wind, snow, fire, 

 insects, game, etc. 



3. iJi'tcrmuiation of ihe Qaalitij of each Wood. 

 a. General. 



It has already been explained, that by the quality of a wood 

 or compartment is understood its yield capacity, as expressed 

 by the quantity of produce, which can be derived from it. 



The yield capacity depends, in the first place, on the 

 locality ; but injurious influences may have interfered \\\W\ 

 the full development of the producing factors of the locality, 

 so that abnormal conditions may be the consequence. The 

 forester distinguishes, therefore, between normal and abnormal 

 quality. The quality is normal, if no extraordinary injurious 

 influences have affected the development of the wood. 



A further distinction must be made between the quality of 

 the " locality" and of the " growing wood " or standing crop. 

 Either of the two can be normal or abnormal. The quality 

 of the locality may be abnormal in consequence of a variety 

 of causes, such as the long continued removal of litter, or 

 excessive exposure to the effects of sun and air currents, which 

 have impoverished the soil ; or in consequence of unfavourable 

 natural phenomena, for instance, if the ground has become 

 swampy, temporarily denuded, or covered with moving sand. 

 An abnormal condition of the growing wood may be produced 



