Segmented taper equations with crown ratio and stand density for Dahurian Larch (<Emphasis Type="Italic">Larix gmelinii</Emphasis>) in Northeastern China |
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Authors: | Li-chun Jiang Rui-long Liu |
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Institution: | JIANG Li-chun LIU Rui-long College of Forestry,Northeast Forestry University,26 Hexing road,Harbin 150040,Heilongjiang Province,P.R. China. |
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Abstract: | Segmented taper equation was selected to model stem profile of Dahurian larch (Larix gmelinii Rupr.). The data were based on stem analysis of 74 trees from Dailing Forest Bureau in Heilongjiang Province, Northeastern
China. Two taper equations with crown ratio and stand basal area were derived from the Max and Burkhart’s (1976) taper equation.
Three taper equations were evaluated: (1) the original equation, (2) the original equation with crown ratio, and (3) the original
equation with basal area. SAS NLIN and SYSNLIN procedures were used to fit taper equations. Fit statistics and cross-validation
were used to evaluate the accuracy and precision of these models. Parameter estimates showed that the original equation with
inclusion of crown ratio and basal area variables provided significantly different parameter estimates with lower standard
errors. Overall fit statistics indicated that the root mean square error (RMSE) for diameter outside and inside bark decreased
respectively by 10% and 7% in the original model with crown ratio and by 12% and 7.2% in the original model with basal area.
Cross-validation further confirmed that the original equation with inclusion of crown ratio and basal area variables provided
more accurate predictions at the lower section (relative heights, <10%) and upper section (relative heights, >50%) for both
outside and inside bark diameters. |
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Keywords: | basal area crown ratio Larix gmelinii nonlinear regression taper equations |
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