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Composite system for estimating tree taper and merchantable volume Segaran, Sandy

Abstract

A composite system for estimating taper and merchantable volume up to 5 inches top diameter is described for plantation grown trees of Eucalyptus robusta over the D[sub 4.5] range of 10 to 24 inches and heights of 73 to 122 feet. The stem profile could be described by the model g = a - bh where g is the sectional area in square feet at sectional height h feet, a is the regression constant and b the regression coefficient. Relations are derived between the easily measured tree parameters of diameter at breast height (D[sub 4.5]), diameter at 10 feet high (D₁₀) and total height (H) with both a and b. As a result, the regression coefficient b, which is a measure of taper, varies directly as the square of the diameter at breast height, the product of the diameter at breast height and total height, as well as, the product of the square of the diameter at breast height and total height. Various formulae are summarised to derive the standing volumes for desired heights or nominated diameters, and diameters at specific heights or vice versa, and collated in Section 8. The relations of a on H, b on H and form factor for total volume (Fv by D[sub 4.5] classes, are graphed and inferences are drawn. Bias in height or diameter estimation is small, similar for each class and not substantial. Further the height bias is in opposite sign to diameter bias. Bias, in estimating merchantable volumes to 5 inches top diameter by the taper model, as compared with that of the volume model for merchantable volume is small and negligible. The overall bias for the sample trees is 0.16 cubic feet, that is, 0.13 per cent of the total sample merchantable volume estimated by the taper model. For the range of basic data investigated, this taper model was found to adequately describe the stem profile.

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