Stem volume ratio equations to variable merchantable limits for sweet chestnut in Portugal

Abstract

The volume is a fundamental dendrometric characteristic that helps estimate the amount and value of wood that can be harvested, and provides insight into land productivity. However, accurately measuring trees for volume calculation is both costly and time-consuming. Therefore, equations that estimate volume based on dendrometric variables, such as DBH (diameter breast height) and total or merchantable height, are highly important for forecasting forest production. However, the total stem volume alone does not indicate the amount of wood available for specific uses, such as sawtimber or biomass. Stem volume ratio equations are essential as they provide flexibility in determining the volume of wood based on the tree's various usage categories and potential changes in market demands over time. These equations allow for alternative options in obtaining volume, considering variable top diameter or height. Forest managers can use these equations to estimate the volumes of multiple logs from a single stem during integrated logging and for forest inventory purposes that require yield estimates by product categories. These tools are scarce, namely for sweet chestnut (Castanea sativa Mill.). Therefore, this study's primary objective was to develop volume ratio prediction equations based on tree dendrometric variables, including DBH and total height, for high forest chestnut stands located in northern Portugal. Both linear and nonlinear regression estimation methods were employed, with data analysis based on information collected from 466 standing trees measured using a Bitterlich’s telerescope for precise volume determination. Model validation involved destructive analysis of 39 felled trees distributed across the existing diameter classes (10-65 cm) in three adult chestnut stands. The study employed the ordinary least squares method to fit several linear and nonlinear equations to select models, with the best-fitting equations presented.The data used in this study were collected with the financial support of the AGRO Program, Project 267: Sustainable Management of Chestnut Forested Areas in High-Forest and Coppice Systems. The authors would like to express also their gratitude to the Foundation for Science and Technology (FCT, Portugal) for providing financial support through national funds (FCT/MCTES) to CIMO (UIDB/00690/2020)info:eu-repo/semantics/publishedVersio