MENSURATION IN FRANCE; 689 



The usual practice is to combine estimating with marking. In this 

 case the officer also directs which trees shall be marked for reservation 

 and of course tallies such trees separately. As this is usually done be- 

 fore the timber is put on the market, the would-be buyer can be fur- 

 nished with data showing exactly how many trees ot each diameter 

 class are for sale. 



Again, it must be borne in mind how different French conditions are 

 from ours. The method appears at first sight expensive and with an 

 uneven distribution of accuracy ; but the expense of the complete diam- 

 eter tally is reduced by the very low cost of guard labor, while the very 

 uniform stands make the preparation of a height curve and the estima- 

 tion of form factor or average taper relatively simple and accurate. 



The French Forest Service (Service des Eaux et Forets) pubHshes a 

 thin note book which contains two types of standard volume tables. 

 These are both "universal" tables — that is, they are applicable to any 

 species. The first gives simply the volume of cylinders of given diam- 

 eters and heights ; the results obtained from this are, of course, reduced 

 by multiplication by a form factor. The second gives the volumes of 

 given diameters, heights, and tapers. It is in principle quite parallel to 

 some of the Pacific Coast cruisers' tables, though its arrangement is not 

 quite the same. The drawback to these tables is, of course, that they 

 necessitate the essentially accurate estimation of either a stand form 

 factor or an average taper. Either of these estimates is relatively sim- 

 ple in France, since there are less than a dozen important forest tree 

 species, and the range of values for each and the modifying effect of 

 such factors as age, height, and the like, are well understood. Some 

 French foresters state, for example, that if a form factor of .65 is used 

 for poor stands and .70 for good, the results should be within 5 per 

 cent of the truth, regardless of species or region. 



Local tables and tables for individual species are frequently en- 

 countered, but they may usually be found on examination to be merely 

 selected or modified values from the tables just described. They are 

 based on tree measurements such as ours, but the results are usually 

 compiled to give either an average form factor or an average taper for 

 the species and region in question. The objections to this method as 3 

 general practice are many and too obvious for enumeration. But, again, 

 French conditions reduce the errors to practical insignificance, for when 

 uniform stands are cut repeatedly at the same definite age the average 

 form factor (or taper) becomes a figure which can be determined with 

 reasonable reliability. 



Growth figures in France seem to be for the most part merely the 



