96 DETERMINATION OF THE INCREMENT. 



same quality. Asa rule, however, a large number of different 

 qualities exist ; hence, in practical forestr}', some concession 

 must be made, by being satisfied with a limited number. 

 These rarely exceed five, and frequently three are quite suffi- 

 cient. The best quality is generally designated as I. quality, 

 though the reverse would be better. 



In proceeding to construct yield tables, it is obviously of the 

 first importance to have a ready method, by which the quality 

 of a locality may be indicated. It has been explained in 

 Sylviculture, that the several factors of the locality, such as 

 the chemical and physical conditions of the soil and subsoil, 

 the climate, etc., do not enable the forester to determine the 

 quality of the locality for forest purposes with any degree of 

 accuracy, and that tlie only satisfactory indication is given by 

 the wood which has been produced on it. In other words, a 

 locality which produces, in a given time, a large volume, is of 

 good quality ; one which produces a small volume, of inferior 

 quality. The volume, then, is in the first place the surest 

 indication of the quality of the locality. 



As it is, however, a somewhat cumbrous process to ascertain 

 the volume, when searching for a certain quality, the question 

 arises, whether one or more of the elements, from which the 

 volume is calculated, would not do equally good service. It 

 has been shown above, that the volume is 



V = s X h X /. 



Of these three elements, the form factor moves between 

 comparatively narrow limits, and it is not suited for the 

 present purpose, apart from the fact, that the volume would 

 first have to be ascertained in order to determine the form 

 factor. Basal area and height together give a sure indication 

 of the quality, that is to say, two woods, which show the same 

 basal area and height, may safely be assumed to have the same 

 volume ; hence, the localities, which have produced them, would 

 be of the same quality. 



If only one indicating element is used, the height is far 



