THE GURNAUD METHOD 241 



similar scheme is where the forest is divided into a number of compart- 

 ments equal to the number of years of the rotation. Then the period 

 is based on the time it takes to get regeneration with a margin of a few 

 years for safety. The compartments, equal in number to the years of 

 the period, and most in need of cutting, are grouped into the periodic 

 block to be cut during the period, and the yield is the total volume in 

 this compartment divided by the years of the period. 



The Gurnaud Method.^^ — The Gurnaud method of yield regulation 

 bases the cut upon the actual growth of the different size classes subject 

 (a) to the condition of the stand and (&) to the judgment of the forester 

 since, according to Jobez, "the interpretation of these figures (the 

 growth) is entirely a personal matter and according to each individual 

 case." 



The growth is secured by adding the present growing stock to the 

 cut for the last cutting cycle; this total is subtracted from the original 

 stand to give the apparent growth. To obtain the real growth the 

 volume of the trees under the minimum size calipered, which grew into 

 the merchantable size classes, is subtracted from the apparent growth. 

 This last step is a new idea in American forest technique; it may be 

 going to an extreme of refinement, and might be questioned. The 

 growth per cent is then figured by dividing the original volume into the 

 real growth. The method demands great technical skill and sound 

 judgment in its application; any method can be made to serve under 

 such circumstances but the Gurnaud formula is especially exacting in 

 this respect. The method was designed for selection forests and where 

 a forest had .the normal growing stock it could be readily applied as 

 could any other formula method. 



The advantages of the method are: (1) It necessitates a frequent and 

 detailed study of the stand by size classes, and allows the forester to use 

 his judgment. (2) The growth is based on the increment of the whole 

 stand and allows for the volume of trees which were too small to be 

 calipered but which grew into merchantable size classes during the 

 cutting period. This avoids the calculations of growth based on the 

 increase in size of individual trees. (3) The trained forester realizes 

 that growth and yield figures are, at best, an approximation.*" There- 

 fore, the best way to avoid errors is to have frequent stocktaking. 



The disadvantages are: (1) It is not a real method of regulating the 

 yield because correct results depend on the art of forestry rather than 

 on definite clear-cut principles. (2) Instead of dividing the real growth 

 by the original volume to get the growth per cent Gurnaud should 

 have taken the mean of the first and second inventories. This error, 



35 Based on the discussion by Huffel, Vol. Ill, Economic Forestiere. 



40 Accroissement d'un Massif Jardine, S. F. de F. C. et B., No. 5, March, 1908, A. S. 



