Abstract:

In this study, the sample data were based on stem analysis of 84 trees from Dahurian Larch (Larix gmelinii) plantations located in Dailing Forest Bureau in Heilongjiang Province. Max and Burkhart segmented taper model was used to model tree stem taper. Parameters estimates of 4 parameters and 2 inflection points were obtained simultaneously using Seemingly unrelated regression procedure in SAS. This model is suitable for describing dahurian larch stem taper based on significant test of parameter estimates and F-test. Then, a nonlinear mixed-effects modeling approach was used to model stem taper based on the base model. The best performances were obtained for this model with parameters b₁ and b₂ as mixed effects when considering plot effects and with parameters b₂ and b₄ as mixed effects when considering tree effects. The mixed-effects models provided better model fitting than original model, moreover, the precision of mixed-effects model when considering tree effects is better than that when considering plot effects. Validation confirmed that the mixed model with calibration of random parameters could provide more accurate and precise prediction.

Key words: Larix gmelinii, stem taper, nonlinear mixed model, fixed effects, random effects