212 



CHAPTER III. 



THE NORMAL AGE CLASSES. 



IT has been stated at page 176, that by a normal dis- 

 tribution of age classes is understood a series of age gradations 

 so arranged, that at all times when cuttings are to be made, 

 mature woods of the normal age are available, and so situated 

 that no obstacles to their cutting exist. This means that each 

 age class must be of the proper extent, and that the several 



B0i t age classes must be properly 



grouped, or distributed, 

 over the forest. 



If a forest is to be 

 managed according to the 

 system of a sustained an- 

 nual yield, it must contain 

 a series of age gradations 

 equal to the number of 

 years in the rotation; the 

 oldest age gradation must, 

 immediately before cutting, 

 have the age of the rotation, 

 the youngest must be one 

 year old, with a difference 

 of one year in the age of 

 every succeeding two gra- 

 dations. 



Example. Assuming the rotation of a coppice wood to be 

 20 years, and the height which the oldest wood reaches in that 

 time = 28 feet, then the 20 age gradations may be represented 

 as in the appended figure 46. 



H 

 t " 



H 



H 

 SJ 



a 



Fig. 46. 



