14 



Tlieoretically the possibility is the productive power of 

 a wooded area expressed in quantity of material. Practi- 

 cally it is taken to mean the quantity of material which, 

 without infringing the rules of forestry, may be felled in a 

 forest, annually or periodically, for the time being. This 

 latter quantity depends on the constitution of the producing 

 stock, and on the relation which the stock bears to the age of 

 exploitation determined upon. If the capital is suflBcient and 

 normally constituted, as in fig. 1 for instance, the possibility 

 is equal to the average annual production over the whole 

 area. If, on the other hand, the capital is insufficient, as in 

 fig. 2 for instance, or superabundant, a quantity of material, 

 less or greater as the case may be than the average incre- 

 ment, must be felled during a certain provisional period 

 until the normal state is reached. 



A forest of 30 acres, wliioh it is proposed to exploit as coppice at 20 years, 

 is found to contain a complete series of growths of all ages from 1 to 20 years, 

 each occupying one aero. Here the possibility would evidently be a crop 20 years 

 old growing on one acre {vide fig. 1). If, however, the crop were constituted as shown 

 in fig. 2, it would be necessary, in order to obtain a sustained and annual yield of 

 wood not less than 20 years old, to make the two crops of 19 and 20 years last for 

 some 10 years, until the crops now 10 years old have attained or approached 20 years 

 of age. The possibility in this case might be fixed during the provisional period as 

 the crop growing on two-tenths of an acre per year, after which it would be in excess 

 of the normal possibility, or certain areas might be cut over when the crop was more 

 than 20 years old until the necessary gradation of ages (fig. 1) could be secured. 



Methods of prescribing the possibility.— As it is impossible to 

 collect the annual production all over the area, it is necessary 

 to prescribe the realisation of the possibility in some practica- 

 ble manner. The realisation of the possibility can be prescribed 

 in three ways, vis., (i) by area, (ii) by the number of trees, 

 and (iii) by the volume of material. The first method is the 

 simplest and is that followed in the case of coppice fellings, 

 the method of clearances, as well as partly in the selection 

 method of fellings regulated by cultural rules. The number 

 of trees to be felled is prescribed in the case of standards 

 over coppice and in the selection method. It is only in apply- 

 ing the method of successive regeneration fellings with thin- 

 nings, and, more rarely, in the selection method, that the 

 volume of material to be felled is prescribed. In actual 

 practice, however, in addition to prescribing the quantity of 

 material the areas in which the fellings are to be made are 

 also prescribed. Practically, therefore, what is prescribed 

 is the felling on a giving area of either the crop, a stated 

 number of trees, or a given volume of material. 



