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 equal 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 
