RATE OF GROWTH. 139 



RATE OF GROWTH. 



The Accretion of a Tree is the Increase in Wood 

 Content as the Result of its Activity During the Grow- 

 ing Periods. The rate of growth is indicated by the increase 

 in diameter, in height, or in mass, and may be considered as 

 annual or as periodic. The diameter accretion is eq^ual to twice 

 the thickness of the annual rings for the desired period, meas- 

 ured on the average radius. The current annual increase in 

 diameter is taken as the average of several years back, as five or 

 ten years. It is determined by counting off the required number 

 of rings from the bark in, and measuring their thickness. Twice 

 that thickness divided by the number of years in the period will 

 give the current annual diameter increase. 



The Height Accretion is Determined by counting and 

 measuring the annual cones which appear in a longitudinal sec- 

 tion, or by measuring the length of log between two cross sec- 

 tions which was grown in the time indicated by the difference 

 in the number of annual rings at the two sections. 



For example: A log is fourteen feet long. The lower end 

 shows 178 annual rings and the upper end 150 annual rings. 

 The difference in the number of these rings is 28, or twenty- 

 eight years were required to grow the fourteen feet in length 

 between the two cuts. The number of annual rings at any cross 

 section indicates the lifetime of that portion of the tree above the 

 section. 



Mass Accretion is the Increase in Volume of the 

 Growing Tree. The volume increase of standing trees can 

 only be arrived at approximately, and is based on the measure- 

 ment of the volumes of trees of different ages; the difference will 

 be the increase for the period. The increase in volume is often 

 calculated as simple interest, but where the mass of the tree is 

 considered as capital, interest is computed as compound. 



The Rate of Mass Accretion of a Standing Tree 

 May be Determined in the following manner: In mature 

 trees the height growth per year is inconsiderable, and may be 

 disregarded for short periods of time. The present and past vol- 

 umes, then, vary as their respective basal areas. Taking twice 

 the width of the rings for the period desired from the present 



