36 



low, is counterbalanced by neglecting the volume of the top for the n 

 years. 



DETERMINING THE ACCRETION OF A FOREST. 



There are several methods employed in determiDing the mass accre- 

 tion of a stand of trees for a short period (from ten to twenty years), 

 during which it may be safely assumed that the number of trees of the 

 stand will not diminish owing to natural thinning (death). Of these 

 the following may be recommended: 



When the growing stock of a forest has been ascertained by means 

 of an average sample tree, then tlie accretion of that tree for a given 

 number of years shouhl be multiplied by the number of trees the forest 

 contains, in order to determine the rate of growth of the forest for that 

 period of time. In case the growing stock of the forest was established 

 by arranging its trees in diameter classes, the accretion of each diam- 

 eter class is determined separately by multiplying the accretion of the 

 sample tree by the number of trees involved in the class. Adding 

 together the accretion of all the diameter classes we obtain a sum which 

 represents the rate of growth of the forest for the period of time in 

 question. 



When the growing stock of a forest is determined by means of a pro- 

 portioual number of sample trees representing each diameter, the accre- 

 tions of the sample trees, calculated for each of them separately, are 

 added together and the sum is multiplied by the quotient obtained by 

 dividing the basal area of the forest by that of all the sample trees. 

 The product gives the rate of growth of the forest during the period for 

 which the accretion of the sample trees was determined. 





