Stem taper function for sweet chestnut (Castanea sativa Mill.) coppice stands in northwest Spain
Despite the economic importance of Castanea sativa Mill. in northwest Spain, studies of its growth and yield are practically non-existent.
A compatible system formed by a taper function, a total volume equation, and a merchantable volume equation was developed for chestnut (C. sativa Mill.) coppice stands in northwest Spain.
Data from 203 destructively sampled trees were used for the adjustment. Outliers were removed with a non-parametric local adjustment, providing a final data set of measurements taken from 3,188 sections which was used to test five taper models (compatible and non-compatible). A second-order continuous autoregressive error structure was used to model the error term and account for autocorrelation. Presence of multicollinearity was evaluated with the condition number. Comparison of the models was carried out using overall goodness-of-fit statistics and graphical analysis.
Results show that the models developed by Fang et al. in For Sci 46: 1–12, 2000 and Kozak in For Chron 80, N 4: 507–515, 2004 were superior to other equations in predicting diameter for chestnut coppice stands.
The compatible volume system developed by Fang et al. in For Sci 46: 1–12, 2000 was finally selected as it provided the best compromise between describing stem profile and also estimating merchantable height, merchantable volume, and total volume and therefore provides the first specific tool for more effective management of chestnut coppice stands.
KeywordsChestnut coppice Volume system Segmented model Compatible equations
The authors thank Forest Services (Government of the Principality of Asturias) and the private owners who allowed the establishment of the permanent plots necessary for the development of the study. The authors are grateful to the University of Oviedo, which provided the validation data.
This study was supported by the Spanish Ministry of Science and Innovation (MICIN) and the Plan for Science, Technology and Innovation of the Principality of Asturias (PCTI) as part of the research project “Forest and industrial evaluation of Spanish chestnut” (VALOCAS).
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