i 4 o FORESTRY 



from thinnings extracted from woods belonging to later 

 Periods. As the amount of material which these yield is 

 apt to fluctuate, one seeks to arrange the woods for thinning 

 by taking a certain proportion by area in hand each year. 

 All woods requiring thinning must be visited at least once in 

 ten years. The' yield which may be expected from these 

 intermediate cuttings is estimated from figures given in yield 

 tables. The tables consist of carefully prepared averages of 

 measurements taken from a large number of cases. 



Then there is the so-called Annual plan of management, 

 which has for its object the arrangement of the actual works 

 of felling, sowing, planting, etc., for the ensuing season, in 

 accordance with the instructions contained in the General 

 and Periodic working plans. It is not in itself a working or 

 regulation plan, but is simply part of the executive work. 



Execution of the Working Plan 



For reasons already stated, schemes which define in detail 

 the management for a whole prospective rotation are im- 

 practicable if the rotation be at all lengthy. Indeed, the 

 working plan should never be considered as something fixed 

 and unalterable. In order to maintain its efficacy, it is 

 essential that it be subjected from time to time to revision 

 and renewal. Revision is a check on the accuracy of the 

 work of the original document ; it has due regard to changes 

 in the objects of management, and, in short, by re-examina- 

 tion, the whole scheme gains in reliability and usefulness. 

 In the event of very extensive damage by windstorm or 

 other depredation, the existing plan may be so interfered 

 with that the preparation of a completely new one becomes 

 a necessity. Of the utmost importance to the accomplishment 

 of the aims of the working plan is a proper system of book- 

 keeping. Records must be kept to show how the various 

 operations have been carried out in order to construct a history 

 of each wood. Accounts are therefore necessary to show 

 the yield in material and money on the one hand, and every 



