74 THE THEORY AND PRACTICE OF WORKING PLANS 



3. BY VOLUME.— BASED SOLELY ON GROWING STOCK. ME- 



THODE DE MASSON. 



(a) Description of Method. — Masson's formula closely ap- 

 proximates that of Von ^Mantel, but is clauned by the French 

 to have been developed independently, although based on the 

 same principles. The formula is: 



2V 

 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 



2V I "i 620 ' 



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



r 160 



(c) Value and Application. — Precisely as in Von Mantel's 

 method (No. 2). 



4. BY VOLUME.— BASED SOLELY ON INCREMENT. BY CUR- 



RENT ANNUAL INCREMENT (SWISS METHOD). 



(a) Description of Method. — This method is described in 

 an anon}Tnous article on Selection Forest ^Management in the 

 Swiss Forestry Periodical for 19 13,* briefed in Forestry 

 Quarterly, Vol. XIII, No. 2, pp. 260-262, as follows: 



" Divide the volume of the oldest size classes by the annual 

 increment of the entire stand. This will give the number of 

 years during which the volume of the oldest size classes must 

 last. If this be forty-five (45) years, then the cut for the next 

 decade would be from one-fifth to one-quarter of the volume 

 of the largest size classes." 



Expressed mathematically : 



Let X = the volume of the size classes below the diameter 

 Hmit; 

 Xi = ihe current annual increment thereon; 



* " Die Betriebsordnung im Plenterwald," Schweizerische Zeitschrift fiir 

 Forstwesen, August, Sept., Oct., Nov., 1913, pp. 234-238, 265-272, 307-313, and 

 339-346. 



