60 PRACTICAL FOREST MANAGEMENT. 



the existing 6 or 12 trees per acre, will result in an enormously 

 increased outturn per acre, and the sooner this desirable result 

 can be obtained, the better it will be. 



(2) Calculation of the yield and increment. 



In working plans or fellings where the yield is fixed simply 

 by area, yield and volume tables naturally are not required. In 

 most of the more important sal forests of the province ; in which 

 some form of Periodic Block system has been or will be introduced, 

 the yield is usually fixed partly by volume (for P. B. I.) and partly 

 by area (for remaining P. Blocks)". An example of the calcula- 

 tion is given in Chapter V under methods of calculating the yield. 



(3) The calculation of reduced areas according to differences 



in quality class. 



The enormous difference in yield capacity between different 

 quality classes renders it essential when allotting areas of different 

 quality to the various periodic blocks, or when fixing the annual 

 yield by area, to make due allowance for the difference in yield 

 capacity if a sustained annual yield is required. A ready indica- 

 tion of the yield capacities of different qualities for different classes 

 of produce is given by the M. A. I. curves. Thus in sal forests for 

 a rotation of 80 years, the yield capacities for timber production 

 between the different qualities will be (vide M. A. I. for timber) 



Quality. 



M. A. I. . 



31 The theoretical application of the yield table to determine the yield of the whole working circle, 

 on the formula. Y=IXAXD (where I = M.A.I. per acre of full stock. A = total area, and D = density 

 of stock) cannot be adopted as it involves the unknown factor D, which in our irregular and open sal forests 

 cannot be ascertained except by complete enumeration of the whole growing -stock. 



