64 VOLUME OF WHOLE WOODS. 



If a somewhat smaller accuracy suffices, the following method 

 may be followed : A number of trees are selected which show 

 about an average diameter and height, their heights accurately 

 measured and the mean taken, which represents the mean 

 height of the class, or wood. In some cases the height of the 

 arithmetical mean sample tree is taken as the mean height of 

 the wood. Good results are obtained by ascertaining the 

 mean height by graphic interpolation. In that case the 

 diameters are plotted as abscissa and the heights as ordinates ; 

 an average line is then drawn between the various points which 

 gives the mean heights for successive diameters. 



It remains to be noted, that the heights obtained by means 

 of these simplified methods are generally a foot or two smaller 

 than that obtained according to the formula : 



S. 



How the form factors of single trees are ascertained has 

 been described above. Similarly form factors for whole woods 

 can be determined according to the formula : 



V=SxHxF, 

 i iS x H 



If volume tables are used, the calculation is made according 

 to the formula : 



V=nxsxhxf. 



Here s x h x f, equal to the volume of the mean tree, is taken 

 direct from the tables. 



Difference 

 in % com- 

 pared with 



The example on pp. 62 and 63 shows : Volume - or( ,* h ry 



Volume calculated with Kunze's form factors according ' method? 8 



to inch classes ........ = 3515 + 1-6 



Volume calculated with mean height of trees arranged 



in four groups ........ = 3502 + 1-2 



Volume calculated with mean height of whole wood . = 3568 + 31 



