FRENCH FIR MANAGEMENT IN THE VOSGES 539 



erty to earn, as, , for example, 3 per cent. Here we have a dangerous 

 circle. Practically the rate results from the yield and from the existing 

 growing stock — two factors which are themselves dependent on the ex- 

 ploitable size — and (consequently) the problem apparently only can be 

 solved by successive uncertainties. In thus proceeding, we have found 

 that when using an exploitable size of .5 meter (diameter) the return 

 in the forest, under consideration and under the conditions described 

 below, will amount to 3.05 per cent. Accordingly, this (financial) 

 diameter of .5 meter has been taken as the exploitable size. Neverthe- 

 less, it is very interesting to know the rate of the various trees of dif- 

 ferent diameter classes ; this is quite valuable in order to determine if 

 the trees .5 meter and above should not be conserved because they are 

 still growing vigorously. To determine this rate, it is necessary to 

 know (a) the time necessary for trees of each diameter class to pass 

 from one class to the next highest one; (b) the stumpage price per 

 cubic meter for (trees of) each diameter class. 



(a) Time necessary for trees of one diameter class to pass to the 

 next higher class. — This time, under (a), varying essentially with the 

 density of the stand, cannot be accurately determined; nevertheless, it 

 is obtained with a certain approximation by analyzing tree boles nor- 

 mally spaced (diameters of crowns equal to fifteen times that of the 

 boles, as explained below). Without making a complete tree analysis, 

 which requires felling and long calcjulation, this can be rapidly deter- 

 mined by means of Pressler's borer . . . without injury to the 

 tree. ... If the ground slopes, the boring should be made parallel 

 with the contour lines because of the phenomena of eccentricity of fir 

 rings ; the number of rings counted on .025 meter will give the number 

 of years which it takes the tree to grow from one 5-centimeter diameter 

 class to another. This method is not accurate, and the less so the fewer 

 trees are used. 



When two inventories are available, the determination can be made 

 more exact, for all the trees of the forest can be counted; for example, 

 a stand whose stock-taking, done at eight-year intervals, is as follows : 



Number of trees 



Diameter, / ^ v Remarks 



centimeters 1900 1892 



20 10,206 6,826 The second column includes the trees 



25 6,521 5,575 counted in 1900 and those which were cut 



30 4,700 3,437 from 1892 to 1900. 

 etc. 



Total 27,559 20,160 



In 1900 there were 27,559 trees of all diameters; in 1892 there were 

 20.160; the difference, 7,399. evidently represents the wood which in 



