35 



thrifty growing tree. Tlie general appearance and the crown develop- 

 ment of the tree will indicate which one of the figures should be taken 

 for calculations. 



DETERMINING THE ACCRETION OF A FELLED TREE. 



The average annual accretion of a felled tree may be determined with 

 greater accuracy , because the volume and the age of the tree can be 

 obtained ^ith more exactness. The age of the tree is established by 

 counting the rings on the stump section and adding to the number 

 counted live or six years, which were required by the tree to reach the 

 height of the stump. 



The current accretion for any given number of years of a felled tree 

 may be determined as follows : 



^ H ^ 



Fig. 12 Determining the current aceretion of a felled tree. 



Find the volume of the felled tree by multiplying its height (H) by 

 the basal area which corresponds to the diameter measured at the mid- 

 dle of the tree (D), bark excluded; then, by some trial, find a place 

 near the top (see fig. 12) where the section {Id) contains as many rings 

 as there are years in the period {n) for which the accretion is to be 

 determined. Then from the middle of the topless portion {d) of the 

 tree extract, with Pressler's accretion borer, a cylinder of wood; meas 

 ure off on that cylinder the width of the last n rings and subtract 

 twice that width from the outside diameter measured here without bark. 

 The dift'erence gives the diameter the tree had n years ago. Multiply- 

 ing the basal area corresponding to that diameter by the length {h) of 

 the topless portion of the tree the volume of the tree as it was n years 

 ago is ascertained. The difference between the present and past vol- 

 umes gives the periodic accretion for the last n years. 



Pressler simplifies this method by measuring at the middle of the 



topless stem ( o ) both the present diameter and that of the tree as it 



was n years ago and calculates the respective volumes by employing 

 the length of the topless stem. The excess in volume which results for 

 the present tree due to the fact that the diameter which should have 



been taken halfway of the full length tree ( at ^ j was measured too 



