Compatible stem taper and volume models for dahurian larch

The study describes the application of compatible nonlinear equation systems in developing stem taper and volume models and methods of parameter estimation. Three compatible stem taper and volume systems with different inflection points were developed for dahurian larch (Larix gmelinii Rupr.) plantations located in Dailing Forest Bureau, Heilongjiang Province of northeastern China based on a Max and Burkhart segmented taper model. Taper and volume systems share the same parameters. To concurrently minimize error in endogenous variables, seemingly unrelated regression (SUR) procedure of the PROC MODEL in SAS software was used to obtain parameter estimates of equation systems. Coefficient determination, absolute bias, relative absolute bias, root mean square error and relative root mean square error were employed to evaluate the precision of different model systems. The results showed that Max and Burkhart segmented taper and volume model systems with two inflection points provided best precision of model fitting. The lower and upper stem inflection points of dahurian larch were found to be 0.09H and 0.77H at tree height for diameter outside bark, and 0.08H and 0.75H for diameter inside bark. Model validation further confirms that this model system provides the best precision of diameter and volume prediction.