Total and Merchantable Wood Volume Equations for Eucalyptus hybrid Trees in Gujarat State, India

Abstract

Eucalyptus hybrid is one of the most important tree species adopted for large-scale commercial plantations by State Forest Departments, nongovernmental organizations (NGOs), and farmers in India. But accurate volume equations are not available. The aim of this study was to develop equations for predicting individual tree total volume and merchantable volume for E. hybrid. A total of 114 trees with ages between 1 and 19 yr and breast height diameter (dbh) between 4.7 and 33.1 cm were felled for model fitting and analysis. Linear and nonlinear equations were used to model the relationship of total volume with dbh, and with dbh and total height of the trees. Merchantable volume equations for estimating merchantable volume to any minimum bole height are also presented. For this, diameters were measured at different heights along the stem including height to the base of crown. The equations tested fitted the data well. The adjusted R2 and root mean squared error indicated that for estimation of V0 from dbh, and from dbh and total height, non-linear equations performed better. These equations may also be recommended for use because of their simplicity and ease of use in the field. In general, nonlinear models only with diameter and with diameter & height overestimated total volume with a mean difference between measured and predicted values of 0.48% and 0.15%, respectively. The variable top-height volume equation tended to underestimate the merchantable volume with an average difference of 1.74% between measured and predicted volume. Model validation with an independent data set indicated that for greater accuracy models should be calibrated with local data. Based on the model validation with sample data and on the models biological logic (volume depends on tree diameter as well as on height), model incorporating diameter as well as height was considered to be more appropriate for general volume estimations.