Wilson Ancelm Mugasha
Accurate estimation of diameter at breast height (D1) is fundamental for reliable assessment of forest volume and biomass. However, in coppiced stands of Eucalyptus spp., the D1 may introduce systematic bias due to stem deformation originating from stumps. This study developed a practical approach to estimate the appropriate diameter to apply (Dc) measured at 1.3 m above the stump height for coppiced Eucalyptus grandis trees in the Sao Hill Forest Plantation, Tanzania. Data were collected from four compartments (18-19 years old), where 200 trees were measured for diameters at multiple positions along the stem, including 0.2, 0.4, 0.6, and 0.8 m above the stump height, as well as D1 and Dc. Results showed that 81-97% of trees were affected (deformed) by coppicing, indicating widespread structural deviation from standard measurement assumptions. Strong linear relationships were observed between Dc and all measured diameters (R² ≈ 0.996-0.998), with regression lines passing through the origin and low standard error. Among the tested variables, D1 proved to be the most practical predictor of Dc due to its ease of measurement and strong correlation. The study established that Dc is approximately 95% of D1, providing a simple correction factor for field application. The proposed method improves the accuracy of forest inventory estimates while maintaining operational simplicity and is therefore suitable for large-scale application in coppiced plantation systems, particularly of Eucalyptus species.