150 COLONIAL REPORTS MISCELLANEOUS. 



Data of the kind mentioned above, to be of any scientific value, 

 should be procured from the average of a large number of obser- 

 vations, and the peculiarities of each species ascertained 

 separately. 



(b.) The Proportion existing between the various Age or Girth 



Gradations. 



Before proceeding to ascertain these ration by means of linear 

 valuation surveys, it will be necessaiy to adopt some system of 

 classification of the gradations. The following will be found 

 suitable for present purposes : - 



In a well-stocked forest the girths of the trees may, with a 

 fair degree of approximation, be taken as directly proportional 

 to their ages ; if, therefore, the girths of the various sizes be 

 equally spaced out between the plants of smallest dimensions, 

 and the average size of the mature trees, a convenient workable 

 scale can be arrived at. This scale need not, for the rough 

 approximations now being considered, be divided into more than 

 three classes. For example, suppose the average girth of the 

 mature tree to be 72 inches, or 6 feet, then the classes (if only 

 three divisions are made), will be as follows : 



The third class (youngest trees) will consist of all plants up 



to 24 inches in girth. 

 The second class (middle-aged trees) will consist of all plants 



between 24 inches and 48 inches in girth. 

 The first class (mature trees) will consist of all trees between 



48 inches and 72 inches and over in girth. 



In this example the girths have been equally spaced out at 



72 



intervals of =24 inches, and the various classes are multiples 

 o 



of this interval. The denominator always denotes the number 

 of classes it is proposed to adopt. 



The actual size of the girth will, of course, depend in each 

 case on the size selected as the average girth of the mature tree, 

 and will vary with the species. Suppose the size of the mature 

 tree is found to be only 48 inches, then if only three girth classes 

 are required, the girths will be spaced out at intervals of 



-5- = 16 inches. So the classes will be: 



o 



Third class : All plants up to 16 by 1 inches in girth. 

 Second class : All plants between 16 inches and 16 inches by 



2 inches or 32 inches in girth. 



First class: All plants between 32 inches and 16 inches by 



3 inches or 48 inches in girth and over. 



The whole object of this division into girth classes being to 

 ascertain the condition of the aye gradations witJi reference to 

 any particular species, the classification of the ages into the 

 tlu-ee divisions, young, middle-aged, and mature, and the sub- 

 sequent determination of the proportions existing amongst the 

 number* of the plants found in each of these classes will be quite 



