Estimation of Merchantable Volume of Eucalyptus Clones Based on Leaf-Level Hyperspectral Data

This study assessed the suitability of chlorophyll, nitrogen, and water content, derived from leaf-level spectroradiometer data, for estimating volume of Eucalyptus clones in KwaZulu-Natal, South Africa. Volume was derived from field measurements of diameter at breast height (dbh) and tree height. Chlorophyll, nitrogen, and water related indices were used to estimate merchantable volume of Eucalyptus clones. Analysis of variance (ANOVA) was used to assess whether significant differences could be detected amongst index values within the plots or compartments, based on different age groups, clones, and site qualities. Cross validation and model selection based on adjusted R² and low Mallows´ Cp were utilized in the development of volume models. The strength of the correlations for all clones combined was found to be much lower than the individual relationships for E. grandis and E. saligna. ANOVA results indicated that volume was significantly (p <; 0.05) influenced by age, site quality, and the clone in question. Models developed using stepwise approach without ancillary data, such as age and site index, had low adjusted R² values (0.47≤ R²≤0.72) and high root-mean-square error (RMSE) values compared to models that included ancillary data (0.81≤ R³ ≤ 0.90). Partial least square regression models exhibited higher R²(0.92 ≤ R² ≤ 0.96) and lower RMSE and Mallows´ Cp. These results suggest that spectral measurements of chlorophyll, nitrogen, and water content have potential as independent variables to assist in the estimation of merchantable volume of Eucalyptus clones. This has important implications since results can be extended to airborne data and regional assessments.