17S THE INCREMENT. 



are comparatively more tapering, while those with the crown 

 restricted to the upper part of the stem show a more cylindrical 

 shape. The form or shape of the stem depends, therefore, on 

 the distribution of the crown. If, with advancing age, the 

 crown of trees in crowded woods moves higher up the stem, 

 the difference in diameter increment between the lower and 

 upper part of the stem decreases, and this is accompanied by 

 what may be called the "form increment"; in other words, 

 the tree becomes less tapering. The forester expresses this, 

 as explained at p. 36, by the " form factor," or the co-efficient, 

 by which the volume of a cylinder of the same base and height 

 as the tree must be multiplied, in order to obtain the volume 

 of the stem of the tree. 



It has been stated, at p. 38, that in practice only the form 

 factors based on a measurement of the base at height of 

 chest, or 4J feet above the ground, are used, and at p. 39 the 

 form factors for the following trees were given : — 



Scotch pine, according to Schwappach. 

 Spruce, ,, ,, ,, 



Silver fir, ,, ,, Lorey. 



Beech ,, ,, Schwappach. 



Oak ,, ,, Wimuienauer. 



These factors refer to trees grown in fairly crowded woods. 



In the case of trees grown in coppice with standards, form 

 factors are out of the question. 



b. Volume Increment of Whole Woods. 



The increment of a wood consists, during the first period of 

 life, of the full increment of the individual trees. As soon as 

 the trees close overhead, the extension of the crowns is inter- 

 fered with, followed by a decrease in the diameter increment. 

 As long as the degree of crowdedness is not too great, the 

 height growth is not reduced ; on the contrary, a moderate 

 degree of density of the leaf canopy encourages height growth. 

 Although, during this period, the individual tree has less 



