35 



The calculation is completed thus (in the field-book itself of the 

 enumeration survey) 



Comportment 11. 



The " contents per tree " are obtained from the tables of form- 

 factors or volumes, as the case may be. 



11. Valuation survey by ocular estimate. 

 Two modes of procedure may be adopted 



1. The contents of each tree of the crop may be estimated, the 

 contents of the entire crop being then obtained by a 

 mere sum of simple addition. Such a procedure, how- 

 ever, takes as much time as a complete enumeration 

 survey based on the actual measurement of the girths 

 of the trees, and once the girths have been measured 

 and recorded, there is very little extra trouble in measur- 

 ing the heights of a few trees and obtaining the contents 

 of the crop by the much ncore trustworthy method of 

 valuation by the richt- height, or with the aid of tables 

 of form-factors or of volumes. 



1L The contents of the whole crop may be estimated en bloc. 



An intelligent forester who has had long local experience 

 in the clean-felling of coupes can often give a fairly 

 accurate estimate of the quantity of produce standing 

 per acre, but the best man is nevertheless liable to make 

 an error of as much as 50 per cent. 



