174 PRINCIPLES OF WORKING PLANS. 



sable articles of life, but it is bulky, and not adapted for a long 

 transport by land. To this must be added that long periods 

 of time elapse between the planting and harvesting of trees. 

 Both these matters make it desirable that the yield of forests 

 should be continuous and brought into the market in annually 

 equal or approximately equal quantities, necessitating a man- 

 agement based upon the principle of a sustained yield. 



Generally speaking, a " sustained yield " is secured, if all 

 areas which have been cleared are restocked within a reason- 

 able time, and the young woods which spring up properly 

 tended, so that the soil continues to produce crops of wood. 

 At the same time a distinction must be made between : 



(1) The intermittent working, if the successive returns are 



separated by a varying number of years. 



(2) The annual working, if final cuttings occur in each year. 



If the latter are approximately equal in quantity year 

 by year, the method is called the " strict or equalized 

 annual working." 



The regulation of the yield of forests worked intermittently 

 is very simple. It is only necessary to ascertain the most 

 profitable rotation, taking into consideration the objects of 

 management, and to make the thinnings whenever they become 

 necessary. 



Although the method of annual working, and especially of 

 the equalized annual working, is not an absolute necessity, 

 still it is in the majority of cases highly desirable, more espe- 

 cially where extensive areas are under treatment, or where a 

 steady market has to be regularly satisfied. Moreover, it has 

 considerable advantages, of which the following may be 

 mentioned : 



(1) It favours the development of a regular and steady 



market, with a sustained competition of purchasers. 



(2) It affords equal employment year after year, and enables 



the administration to maintain a regular number of 

 workmen, and to instruct them thoroughly in their work. 



