THE DETERMINATION OF THE ROTATION. 



91 



be taken as near 4| feet as possible, the calliperman stands on 

 fehe upper side of the tree if on hilly ground, one diameter 

 measurement suffices. 



By rotation is meant the predetermined time period during 

 which it is intended to cut over a working circle. 38 Rotation 

 really refers to even-aged crops. As regards solitary trees or the 

 individuals of a canopied crop considered singly the age at which 

 they become exploitable varies from tree to tree according to the 

 special environment of each, and in such cases the exploitable size 

 is of more importance than age. Nevertheless in a selection 

 forest a rotation calculated to produce an average exploitable tree 

 must be determined for the purpose of calculating the yield, but 

 this average tree will vary according to the different quality classes 

 of different sites. 



The first essential of a rotation is that it produces a crop of 

 trees for which a demand exists and the second that this particu- 

 lar class of crop shows satisfactory financial results. It is useless 

 growing coppice for firewood when there is no demand for this 

 material, nor is it profitable to produce small low class material 

 when the local market demands high class saw logs and is pre- 

 pared to pay for them. 



The text-books deal with the various rotations and the way in 

 which they are calculated ; it is only proposed here to give practi- 

 cal examples of how this matter may be considered. It has been 

 shown in Chapter IV how the preparation of yield tables simplifies 

 the calculation of the rotation and renders it a simple matter to 

 fix the rotation showing the greatest volume production, whether 

 of firewood and small timber or sawn scantling. 



' The sal yield table (in three quality classes) has been given 

 in Chapter VI (Part I) and should be referred to. From the yield 

 table it will be seen that the M. A. I. is practically constant for II 

 and III Qualities between 80 and 90 years (excluding establishment). 



38 *Chc 'Cheory and 'Practice of Working 'Plans. RECKNACEL- 



The 



determi- 

 nation of 

 the 

 rotation. 



Calcula- 

 tion of the 

 rotation 

 for sal in 

 Dehra 

 Dun. 



