61 MEASUl{E:\rENT OF WHOLE WOODS. 



that they are applicable to the Midland Counties, and prol)aljly 

 also to districts further north. 



It will be seen, tbat, for the methods described above, the 

 greatest difference amounts to 1"7 per cent. Under these 

 circumstances it appears, that any of the methods meets 

 the requirements of measurements for the preparation of 

 working plans, and that much more depends on the care 

 bestowed upon the operation than on the particular method 

 followed. If the actual fellings show greater differences tlian 

 the calculations justify, they are frequently due to extraneous 

 causes, such as the felling of the trees at some distance above 

 the ground, careless working up of the material, inaccurate 

 measurement of the fall, theft of material, etc. 



In all cases, where special accuracy is required, as for 

 instance for scientific investigation, or for the determination of 

 the sale value of woods, the classes, or groups, should be small 

 and the number of sample trees large. In this way greater 

 accuracy is likely to be obtained than by making a distinction 

 between the different methods, which have been described. 

 Above all, the utilisation of form factors is strongly recom- 

 mended, especially as there are now callipers to be had, which, 

 ^^hen measuring the diameter, give the basal area of all the 

 trees, which have been measured. Of these, Wimmenauer's 

 calliper can be specially recommended. Where form factors 

 are not yet available, efforts should be made to collect the 

 necessary data for their preparation at the earliest possible 

 date. Their application obviates the cutting down of sample 

 trees, and the determination of the volume takes only a 

 fraction of the time required in the case of any other method. 

 In the absence of form factors, or volume tables, Urich's 

 method is the most useful. 



11. — The Height is not a Function of the Diameter. 



If it is found, that, in the case of equal diameters, the heights 

 differ considerably, then height classes must be formed in 

 addition to diameter classes. 



