85 



CHAPTEK III. 



MEASUREMENT OF STANDING TREES. 



1. Ocular Estimate. 



Originally, the volume of standing trees was estimated. 

 Such an estimate takes into consideration the special shape or 

 form of each tree, and fixes the volume accordingly. The 

 accuracy of purely ocular estimates depends entirely on the 

 person, who makes them. To be only approximately correct, 

 the estimator requires great practice and occasional oppor- 

 tunities to compare his estimates with actual measurements, 

 after the trees have been felled. Even then the results are 

 subject to considerable errors, unless the estimator practises 

 his art constantly. Mistakes of 25 per cent, are of common 

 occurrence, and they may reach up to 100 per cent, in the 

 case of an inexperienced estimator. 



The uncertainty of purely ocular estimates led to the 

 measurement of diameter (or girth) and height; this done, 

 the basal area near the ground can be calculated, multiplied 

 by the height and an estimate made of the actual volume of 

 the tree. It stands to reason, that such an estimate is less 

 dependent on the individuality of the estimator, than that 

 mentioned above, since he has only to estimate the proportion, 

 which exists between the actual volume and that of an 

 imaginary body constructed out of the height and the sectional 

 area at the base, a matter which he must decide according to 

 the peculiar shape of the tree. By degrees it was considered 

 desirable to collect data regarding the form of various trees, 

 which might be utilised in subsequent estimates, and thus 

 foresters arrived at the method next to be described. 



n 9. 



