150 transacnons of royal scottish arboricultural society. 



Influences Tending to Decrease the Form-factor, 

 i.e. an increase in girth or heiglit without a corespond- 

 ing increase in volume. 



1. Volume increase taking place largely in the lower part of 

 the stem. This probably occurs where trees are grown in the 

 open and when the crowns have great depth. 



2. Increase in girth due to the abnormal swelling from the 

 root reaching up to breast-height. 



Trees may have a natural tendency towards the paraboloid 

 form at one period in life and towards the neiloid form at 

 another. Hiiffel states that the form of trees is first neiloid, 

 passes to a true cone, and finishes as a paraboloid. If so, such 

 a tendency, together with other causes, e.g. exposure, is bound 

 to modify the theoretical trend of the form-factor as explained 

 above, but nevertheless, the mathematical variation shown 

 always exists and is almost certainly of greater relative import- 

 ance. Form-factor curves of stands, when the form-factor is 

 plotted against the girth, usually show the trend indicated, 

 though other causes may raise or lower the form-factor of the 

 wood as a whole, so that one stand may reach its maximum 

 sooner or later in life than another, while the maximum form- 

 factor of one stand may be higher or lower than that of another. 

 For young woods, until most of the trees have passed the 

 culminating point in the curve, the breast-height form-factor is a 

 very uncertain index of taper. For middle-aged and mature 

 stands of the same species it becomes in this respect more 

 useful, especially if the mean-height and mean-girth of these 

 stands are taken into account. It is not, then, a true expression 

 of taper, especially for young woods, and cannot be used in- 

 discriminately in the comparison of stands. It would be wrong, 

 for example, to compare the form-factor of a 15-year-old larch 

 plantation, which is probably at the stage when its form-factor 

 is at a maximum, with that of an 80-year-old Douglas fir wood, 

 in which the form-factor has been slowly decreasing for some 

 years, not to mention the large bark development in old trees, 

 and so in this way conclude that the taper of the first subject is 

 better than that of the last, because of its higher form-factor. 



What has been said above in no way detracts from the value 

 of the form-factor as a reducing factor for ascertaining the 

 volume of stands, and such is its chief use in practice. It has 

 also much value in another respect. 



