Use of stand density to improve prediction performance of stem taper model for Taurus cedar

• Main Authors: Ramazan Özçeli̇k, Onur Alkan
• Format: Article
• Language: English
• Published: Isparta University of Applied Sciences Faculty of Forestry 2020-06-01
• Series: Turkish Journal of Forestry
• Subjects: stem form; mixed-effects modelling; calibration; stand density; variable-form taper model; gövde formu; karışık etkili modelleme; kalibrasyon; meşcere sıklığı; değişken şekil gövde çapı modeli
• Online Access: https://dergipark.org.tr/tr/pub/tjf/issue/55599/705719?publisher=iubu

Taurus cedar (Cedrus libani A. Rich.) is economically and ecologically one of the most important forest tree species in Turkey. In this context, knowing the state and limitations of growth and yield of Taurus cedar forests is necessary for improving future management and planning strategies of timber resources. Individual tree volume estimations are one of the most important tools in growth and yield prediction models of the tree species. The use of taper equations in estimating tree volume has recently become useful tool. Taper equations are used to estimate diameters along the bole at any given height and these models are basic pre-requisite to estimating individual tree volumes and product yield. The previous studies showed that, stand characteristics, such as stand density, regeneration method, soil type, and geoclimatic attributes also may have significant impact on tree growth and stem form. Therefore, it makes sense that including stand density information in stem form models should improve model performance in stem diameter and volume estimations. </span></div><div style="text-align:justify;"><span style="font-size:12px;">In this study, the effects of stand density on stem form were examine and to develop taper equations that incorporate stand density information using nonlinear mixed-effects modeling approach for natural cedar stands in West Mediterranean Region of Turkey. As a result, the predictive accuracy of the model was improved by including stand density as covariate. In addition to, diameter measurements from various stem locations were evaluated for tree-specific calibrations by predicting random-effects parameters. It was found that an upper stem diameter at 9.3 m above ground was best suited for calibrating tree-specific predictions of diameter outside bark.