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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:
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