Service Forester's Handbook

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====== Growth Calculation & Projection ======
Use the following method to determine the growth percent using basal area.
This method can also be used to project basal area, diameters, and volume.

Procedure: Use a prism, bark gauge and a diameter tape to obtain growth
information from a representative sample of trees (preferably all the 
trees within prism range at pre-selected points; for examle, every fifth point).

    The following information is obtained from each tree:
    
    a. Radial bark thickness
    b. Diameter at breast height (D.B.H. outside bark)
    c. Radial growth during the last 5 years (have the data or estimate it)
    
D.I.B. (D. Without bark) = D.O.B (D. With bark) - 2 X radial bark thickness.\\

d.i.b. = D.I.B. - 2 X radial growth during last 5 years\\    

The term: Σ(d.i.b./D.I.B.)2  is the ratio of basal area 5 years ago to the present basal area.\\

Example:
^Tree No. ^D.O.B  ^D.I.B  ^d.i.b.  ^d.i.b./D.I.B.   ^Σ(d.i.b./D.I.B.)2 |
|1        |8.4    |7.6    |5.8     |.763            |.582              |
|2        |6.7    |6.0    |4.0     |.667            |.445              |
|3        |10.2   |9.3    |7.8     |.839            |.704              |
|4        |12.0   |11.0   |9.6     |.873            |.762              |
|5        |9.6    |8.7    |6.8     |.782            |.612              |
^Total                                              ^3.105         ^^^^| 

% growth = 1 - (Σ(d.i.b./D.I.B.)2 /total trees in sample)\\
% = 1 - (3.105/5) = 1-.621 = .379\\
% = .379 or 37.9% (for 5 years)\\
% annual growth = 37.9/5years = 7.58%\\

^Present                               ^Projected to next 5 Years     |
|(Basal Area)                          |(Basal Area Increase)         |
|(Volume) X 37.9% =                    |(Volume Increase)             |
|(Average Diameter)                    |(Average Diameter Increase)   |

Example: Estimated volume at end of 5 years:
<file>
Present volume/acre           = 1450 board feet
% growth in 5 years           = 37.9%
Increase in volume in 5 years = 550 board feet
Present volume/acre           +1450 board feet
Volume/acre at end of 5 years =2000 board feet
</file>
Service Forester's Handbook

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