9 



langtiage. Forestry could be very well condncted without employing any of the above 

 terms. 



The crop in a forest is said to be exploitable when it has 

 attained the condition that is required in order to fulfil the 

 purpose with which it is worked. The age of the trees when 

 this condition is reached is called the exploitable age. 



Thus, a forest exploited for quantity of fuel, or timber to furnish sleepers, would 

 be expoitable when, the capital being properly constituted, the oldest trees were large 

 enough to furnish in jfreatest quantity the fuel or sleepers of the size desired. The 

 age of the trees, when this condition is reached, would be the exploitable age. Simi- 

 larly, a forest exploited in view to the realisation of the highest rate of interest in 

 the capital invested would be exploitable at the age when this object was attained. 



The exploitable age also expresses the time required by 

 new growth, in a crop which, is being generated, to attain 

 exploitable dimensions. 



The use oE the words rotation or revolution (Fr. revolution) to express the exploit- 

 able age is due to the fact that, under the methods of trpatment vei-y generally in 

 use informer days, the interval of time between successive fellings in the same area 

 was the number of years in the exploitable age. At present this is generally only true 

 in the case of coppice. In most other oases the fellings pass over the area several 

 times during the course of the so-called rotation. This word is therefore confusing, 

 and will be used in these pages only to express fhe felling rvtation. When referring 

 to the age at which the trees are felled the term exploitable age will be employed. 



The age at which frees are felled in properly managed 

 forests is not, however, always the exploitable age. Owing 

 to irregularities in the composition of the forest capital it 

 frequently happens that, during a longer or shorter period 

 which may, and strictly speaking ought to be, the same length 

 as the exploitable age, trees or crops must be felled before 

 or after they become technically exploitable in order that 

 the correct proportion of age-classes may be secured. 



Calculation of the exploitable age. — The price and the utility 

 of wood depends, as a rule, on its dimensions, that is to say 

 on the age of the tree when .felled. In order to determine 

 the exploitable age in a forest exploited for its wood, it is 

 suflScient for present purposes to ascertain the size of the 

 trees that will furnish the greatest quantity of the most 

 useful produce, i.e., that will bring in the highest price or 

 yield the highest rate of interest on the capital invested. The 

 average age at which the trees attain this size can then be 

 determined by observation. Where the trees are simply pre- 

 served with a view to indirect benefits, such as the shelter 

 they afford to the soil, the exploitable age will generally 

 approach their natural longevity. 



