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CHAPTER VI. 



DETERMINATION OF THE INCREMENT. 



DURING every growing season a tree increases by the elonga- 

 tion of the top shoot, side branches and roots, and by the 

 laying on of a new layer of wood and bark throughout its 

 extent. Thus the height and diameter (or basal area) as well 

 as the spread of the crown increase constantly, up to a certain 

 age, producing an increase of volume called the increment. 

 By adding up the increase of the several trees in a wood, that 

 of the whole is obtained. 



The increment may refer to one or more growing seasons, 

 and accordingly a distinction must be made between : 



(1) The current annual increment, or that laid on in the 



course of one year. 



(2) The periodic increment, or that laid on during a number 



of years or period. 



(8) The total increment, or that laid on from the origin 

 of a tree or wood, up to a certain age, frequently that 

 when the tree, or wood, is cut over. 



(4) The mean annual increment, or that which is obtained 

 by dividing the increment laid on during a given period 

 by the number of years in the period. If the mean 

 annual increment is calculated for a portion of the total 

 age, it is called the periodic mean annual increment, 

 if for the total or final age of the tree, or wood, it is 

 called the final mean annual increment. 



In determining the increment of whole woods, it must be 

 remembered that a certain number of trees disappear from time 

 to time owing to thinnings and natural causes. All such 



