QUALITY CLASSES OF YIELD TABLES. 99 



accuracy, and that the 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 indi- 

 cation 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=sxkxf. 



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 

 preferable to the basal area. While two woods which have the 

 same basal area may have very different heights, experience 

 has shown that two normal woods of the same height have 

 approximately the same basal area. It follows that the height 

 is, next to the volume itself, the best indicator of the qualit^y of 

 the locality. Great height growth means good quality, small 

 height growth inferior quality of locality. 



Neither the mean diameter nor the number of trees can be 

 used for the above purpose, as they are not in due proportion 

 to the volume. Nor can the product of number of trees multi- 

 plied by the mean diameter be used. 



H 2 



