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CHAPTER VI. 



DETERMINATION OF THE INCREMENT. 



During ever}' 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 increment 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. 

 (3.) 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 

 i\\Q; 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 

 removals must be taken into account in determining the total 

 increment laid on. 



