FOREST MANAGEMENT 125 



Increment 



In order to determine the rate of accretion of a given 

 wood from the date of measurement to the time when felling 

 will take place, either the system of increment percentages or 

 that of yield tables is adopted. The former is most useful 

 when it is wished to determine the increment for a short 

 period only, say ten years ; for longer periods than this the 

 latter is more applicable. 



Of the various formulas for ascertaining the rate of incre- 

 ment, that of Schneider is the simplest. It is expressed as 



.-40Q 



The numerator 400 is here a "constant," which in the 

 case of vigorously growing woods must be increased to 500 

 or 600 ; d is the actual diameter in centimetres without bark, 

 and n is the number of annual rings in the outermost 

 centimetre of the stem measurement being taken at breast 

 height, and usually with the help of Pressler's increment borer. 



Yield tables show the progression of a wood's growth per 

 acre by giving the volume of the trees forming the principal 

 part of the crop, the returns from thinnings, and the factors 

 which determine the volume (height, number of stems, basal 

 area). They are founded upon a careful collection of statistics 

 regarding the important species. In the tables the latter are 

 arranged according to the quality of the locality, most usually 

 into five classes I. denoting the best, and V. the poorest 

 condition. 



The term " quality of locality " signifies the yield capacity 

 of the situation the timber volume which under proper 

 management and without accident a crop of trees is able to 

 produce. Height growth gives the surest indication of the 

 quality of the locality. Under ordinary circumstances, there- 

 fore, it is sufficient merely to find the average height and age 

 of the trees in order to assign the wood to its suitable class. 



