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    There have been numerous approaches to modeling stem form in recent decades. The majority have concentrated on the simpler coniferous bole form and have become increasingly complex mathematical expressions. Use of trigonometric equations provides a simple expression of taper that is flexible enough to fit both coniferous and hard-wood bole forms. As an illustration, we applied trigonometric taper equations to examples from thinned and unthinned slash pine (Pinus elliottii Engelm. var. elliottii), willow oak (Quercus phellos L.), and sweet gum (Liquidambar styraciflua L.). Comparison of new trigonometric models with a segmented-polynomial approach developed in 1976 indicates that equations based on trigonometric functions perform equally well and have real advantages in terms of parsimony.

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    Thomas, Charles E.; Parresol, Bernard R. 1991. Simple, Flexible, Trigonometric Taper Equations. Can. J. For. Res. 21: 1132-1137

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