64) 



factors in the Fame iray as the solid contents of »mall wood, Experiiuents give 

 from 0'3 to 0'4 as the aVeiage factor for bark. It has been found that the quantity 

 of bark vaiies from 6 to ]5 percent, of the total volame of the tree or crop. 



There is in India only one practicable method of arriring at the contents of 

 standing trees, namely by means of form-factors. By form-fact<ir is meant the pro- 

 portion which the true contents or volume of a tree bears to a cylinder having the 

 same basal area and height. In other words, the cubical content of a tree is equal to 

 some fraction (/) of the ideal cylinder whose basal area is equal to the section of the 

 tree at bi east-height and whose height is that of the stem. 



Form-factors may be deduced, according to the requirements of the case, for the 

 whole tree, for the stem only, or for the branches. 



It has been supposed th&t the sectional measurements have been tahen at the 

 height of a man's chesr, assumed, for the sake of uniformity, to be 4 feet 6 inches 

 above the ground. But it is obvious that any other conventional height wonld serve 

 the pnrpose, although it is usual and most convenient to employ the one we have 

 adopted. We need refer to only one other convention which is sometimes used. The 

 diameter may be measured at a constant fraction (say, fur instance, one-twentieth) 

 of the height of the tree, in which cai^e the form-factors obtained are termed normal. 

 Kormal form-factors yield perfectly correct results ; but they are not practical owing 

 to the difficulty and trouble of measuring at various heights from the ground. Form- 

 factors are said to be absolute when the base of the ideal cylinder is assumed to be in 

 the same horizontal .plane as the diameter or girth mRasured, In this case the con'- 

 tents of the portion of the stem below the plane must be calculated separately. 



As may be supposed, calcuiations based on form-factors give better results for an 

 entire forest than for individual trees. The preparation of a complete set of form- 

 factors requires grtat care and experience, as ultimate accnracy depends entirely on 

 the selection of the type-trees, whose dimensions serve as the basis of all the calcula- 

 tions. In some cases the trees of a crop have been grouped into various classes accord' 

 ing to their height and shape, and a separate form-factor calculated for each class. 

 Th« most recent inveEtigations prove that form-factors vary chiefly with, the height 

 of the trees. 



T»king into consideration the precent conditions of forestry in India, tLe 

 method of calculating the volume of sample trees by means of Volume tablet, or the 

 Tolnme of the growing stock on a given aiea by means of Yield tables need not be 

 entered into here. 



Section VII.— Calculation of the exploitable age. 



1. General rules.— In order to calculate the exploitable age 

 of a tree it is necessary to ascertain the girth or diameter at 

 ■which it furnishes the greatest quantity of the most useful 

 material that is required. As a rule the price is the best 

 gauge of the utility ; so that in most cases it may be said 

 that trees are exploitable ■when, after deducting all expenses 

 of exploitation, the price they realise per unit of volume is 

 the highest obtainable. 



It not infrequently happens in India that it has to be decided — not what is the 

 price or what is the nKst useful produce but — whether the people in the vicinity of 

 the forest or tht general ci mmnnity should enjoj the produce. The people in the 

 ' neigl bonrhood nay requiie small wtod-fuel and pasture for theii cattle; the general 

 conin. unity, large timber. As a rule, the decision gees in favour of the local wants, 

 thongh this could rot always be defended fiom apurely eccmcimic point of view. It is, 

 moreover, frequently overlooked that in growing laige timber, small timber from the 

 thinnings ai^d branches is also iivailal le generally in as gieat abundance as can be 

 cciiBonied within the radius to which it -nay be pn fitably transported; when more 

 griiziiig can be )rovided thjan if the crqp were cut when young and the forest, conse- 

 quently, dosed mere frequently to cattle. 



