BY YIELD TABLES. 



107 



as number of trees, diameter, form factors, basal area and 

 height, the last is the most suitable. Indeed, actual investi- 

 gation has proved, that, in the case of all woods of middle age 

 and upwards, the volume of two woods, other conditions being 

 the same, is fairly proportionate to their mean heights. The 

 mean height is, therefore, an excellent indication of the 

 quality class ; it, as well as the age, is comparatively easy to 

 ascertain. In selecting the appropriate yield table, the mean 

 height is used in the same way, as has been described for the 

 volume. If the height agrees with one of the heights given 

 in the yield table for the same age, the increment can be 

 read off directly. If it differs, the nearest is selected and the 

 increment of the table modified in proportion to the difference 

 between the actual height and that given in the table. Should, 

 moreover, the wood not be fully stocked, then the increment 

 given in the table must be further modified in the manner 

 mdicated above. 



The height by itself is no true indicator of the quality for 

 very young woods ; for such, as well as for blanks, other woods 

 growing in the vicinity must be utilised, or the soil and 

 climate examined. 



Example: — 



A Scotch pine wood has a height of 53 feet when 60 years 

 old, and a volume of 3,800 cubic feet ; find the probable 

 increment for the next ten years '? 



Yield Tables. 

 (See Appendix IIL) 



The wood belongs to the II. Quality. 



