FORM-FACTOR IN CONIFEROUS TREES. 



151 



Investigation into the behaviour of the form-factors of trees 

 which are true cones, but have different degrees of taper, 

 brings out some interesting points. The greater the degree of 

 taper the shorter is the tree and the shorter is the tree-point. 

 This is illustrated in Figs. 21, 22, and 23. The result of this 

 is that, in trees of the same girth, those with the greater 

 degree of taper have the higher form-factor. This being so, it 

 is obvious that a high form-factor for one stem may not 

 necessarily indicate that it has less taper, or " carries its girth 

 better than," another stem of less form-factor. On the contrary, 

 it may indicate that the latter stem tapers less rapidly than 



rs-Z). 



Ti^U. 



Tis2J. 



the former. It is interesting to observe that the form-factors 

 for the poorer classes of spruce and larch in the British Yield- 

 tables are considerably higher than in the better quality 

 classes. This is shown graphically in Fig. 20, and is pre- 

 sumably due to the relatively poorer height-growth of the 

 former classes in comparison to the girth development. They 

 taper more rapidly, yet their form-factors are higher. 



Another important point of interest is brought out in 

 connection with the measurement of the volume of sample 

 plots in woods by the method of selected sample stems, where 

 the basis of selection is basal area or girth. If too tall a tree 

 is selected, though the volume tends to be too large, the form- 

 factor will have a tendency to be too small, and vice versa, if 

 the tree is too short. Any method, therefore, of measuring 

 by means of sample stems the volume of sample plots which 

 could combine the use of the form-factor along with the height 



