61 

 Section VI. — Calculation or the volume or 



MATERIAL. 



1. Calculation by means of tlie mean sample-tree or type-tree.— 

 The number of trees in each size-clas'S having been ascer- 

 tained, either by counting and measuriag each individual 

 tree in the whole area or by means of sample plots or 

 linesj the volume of material in each class and, conse- 

 quently, ia the whole crop, may be calculated when 

 required by means of sample or type-trees, as follows : — 



We may assume that, on an averaije, in one and tbe same 

 crop, trees of the same diameter and. height have the same 

 cubical contents, Por all practical purposes, tJaerefore, we 

 may assume, without any great error, that if we select trees 

 that are representative of each size-class, ascertain their 

 contents and multiply this figure by the number of trees in 

 the class each represents, the sum gives the volume of 

 material in the whole crop. Such trees are called sample' 

 trees or type-trees, and may be selected either by eye, by 

 taking an average-tree, fairly representative of the crop or 

 class as regards size or, more accurately, as follows : — 



Calculate, with the aid of tables, the sectional areas at 

 the base, where measured, of all the trees in the size-class 

 and total the whole. Divide this figure by the total num- 

 ber of trees in the size-class, and the quotient will be the 

 basal area* of the type-tree required. Calculate the 

 diameter corresponding, to this basal area ; fell several 

 trees of this diameter and ascertain their contents by actual 

 measurement. The mean of their aggregate contents 

 multiplied by the total number of trees in the size-class will 

 give the total volume of material in that size-class. Pro- 

 ceeding in the same way with each size-class, the sum of 

 the volumes obtained gives the total volume of material 

 in the whole crop. 



The Tarionsi modifioations of the methnd above described for the selection of 

 tbe mean sum pie-tree, and tbe varioQH methods of detennining the volnme of sample- 

 trees are dealt with in any treatise on Forest Mensuration.f The following abridged 

 directions in regard to the measurement of trees (.with some considerabU omisitious) 

 may be fonnd nsefal : — 



The hsights of standing trees are ascertained by means of special instruments, 

 designed for the purpose and known as dendrometers and bypsometars. These 

 instraments are of two kinds: — 



* By iatal area is meant the area of the section of the sten of a tree measured on a 

 plane at right-angles to the axis of the stem and at breast-height, or, as is usually taken 

 at 4| feet from the ground. 



•(■ The following works may be consulted :— 



"Memuration oj T imber and limler Crops " by P. J. Carter, obtainable at the ofSce 

 of the SnptiinteEdtnt, (itvtrrn ent Priitirg, Tndis, Calcutta; and f-o Koh's " Mattual 

 of Forestry," Volume III, published by Bradbury, Agneir and Co,, Losdon.i 



