SECTIONAL TRANSACTIONS.— K*. 407 



DEPARTMENT OF FORESTRY (K*). 



Thursday, September 4. 



Remarks by Sir John Stirling-Maxwell, Bt. 



Mr. D. W. Young. — Cultivation of Hardwoods. 



Mr. A. Howard. — Our British Grown Hardivood Trees and Timbers. 



Prof. D. H. Campbell. — The Preservation of the Red Wood Forests in the 

 Western States. 



Afternoon. 



Mr. J. Macdonald. — The Measurement of Standing Trees. 



The necessity for a satisfactorj^ method of measuring standing trees has become 

 clamant in sample plot work in Great Britain, as it is no longer possible in many of 

 the plots to fell sample trees for the purposes of measurement. Apart from scientific 

 work, a good method of measuring standing trees is necessary for ordinary commercial 

 work. The following methods are possible : — 



A. By ocular estimation. 



This is the method most widely used in practice, and in the hands of expert 

 practitioners is capable of considerable accuracy. 



B. By direct measurement. 



This involves climbing the tree and measuring the actual heights and girths. It 

 is possible in onty a small number of cases, and need not be seriously considered. 



C. By indirect measurement. 



i. By measurement with dendrometer. 



This method can be quite accurate, but is inconvenient in practice, e.g. in dark 

 woods, in windy weather, &c. Not generally suitable. 



ii. By volume tables. iii. By form factor tables. 



These method.?, the former commonly used in the United States and the latter in 

 Germany and other continental countries, may be used to estimate the volume of an 

 individual standing tree, but are properly applicable only to whole woods. There 

 is thus the possibility of serious error in applying the tables to individual trees. 



The commonest and most accurate type of volume table gives volumes for 

 trees of different heights and diameters. They assume that all trees with the same 

 diameter (or girth) at breast height and the same height have the same volume. 

 This is not so, as the third factor on which volume depends, namely taper or form, 

 is neglected, and it is this omission that makes the tables inapplicable to individual 

 trees. 



iv. By the form-point method and form-class volume tables. 



Recent work on mensuration has been concerned largely with the idea of form and 

 form-class, and in most of the work trees with the same rates of taper have been 

 grouped together into 'form-classes.' Trees in the same form-class, with the same 

 rate of taper, the same breast-height diameter (or girth) and the same total height are 

 certain to have very similar volumes ; for this reason volume tables based on form- 

 class can be applied with some confidence to individual trees. The one difficulty 

 with standing trees is in determining the form-class. In Sweden Tor Jonson dis- 

 covered empirically a relation between the form-class and the ' form-point,' which is 

 situated at the centre of gravity of the crown. This form-point can be determined 

 with practice quite easily, and when it is known the form-class also is known. 



This method appears to give satisfactory results in the open woods of Scandinavia, 

 but it can rarely be applied in our dense plantations. Some other method of obtaining 

 the form-class is therefore necessary. 



v. By partial measurement and the use of stem curve. 



In the method now being tested it is proposed to measure actual girths on the 

 stem as far up as possible, and for the remainder of the tree to obtain the necessary 

 girths by interpolation on the appropriate form-class curve. The measurements on 



