72 THE THEORY AND PRACTICE OF WORKING PLANS 



2. The method is too strait-laced to permit the free 

 play necessary for the best silviculture, e.g., natural reproduc- 

 tion. 



It is, therefore, restricted in its direct application to forests 

 with fairly uniform conditions, i.e., to coppice, coppice with 

 standards, and well-developed selection forests. As an " area 

 check " on volumetric determinations, however, it finds a wide 

 use. (See Method No. 14 for examples.) 



2. BY VOLUME.— BASED SOLELY ON GROWING STOCK. VON 

 MANTEL'S METHOD. 



(a) Description of Method. — This is the simplest of the 

 " formula methods." Indeed it is hardly to be ranked with 

 them except in having the same underlying principle, namely, 

 that the actual cut must bear the same relation to the actual 

 growing stock as the normal cut (or, what is the same, the normal 

 increment) bears to the normal growing stock. 



Von Mantel considers that the growing stock = the real incre- 

 ment (mean annual) multiplied by half of the rotation (**X-| 



for under normal conditions the volume present (growing stock) 

 in any one year equals one-half of the total volume produced 

 during the entire rotation. This is shown diagrammatically 

 on the next page. Since the volume present (growing stock) 

 need be but one-half the total volume produced, therefore 

 the annual cut = volume present -^ by half the number of years 

 in the rotation, or, as Von Mantel puts it: 



Y (annual cut) = — . 

 r 



(b) Example. — A forest contains 6810 M. feet board measure 



of spruce and fir to be managed on a 160-year rotation. The 



, , V 6,810 6,810 o r ^ u J 



annual cut = — = = — = 85,125 feet, board measure. 



£ 160 80 ^' ^ 



2 2 



