Formfaktor- und Volumengleichungen für den Salbaum (Shorea robusta) im westlichen Tiefland von Nepal

Precise and accurate prediction of tree volume is important to quantify growing stock and to support decision making for sustainable forest management. This study was carried out to estimate the form factor and to develop volume prediction models of Shorea robusta. We selected 48 sample trees from the Western low land of Nepal through purposive sampling. The diameters at 0.3 m, 0.8 m, 1.3 m and 1.8 m above the ground level were measured before felling the trees. After felling the diameters were measured at 2.8 m, 4 m, 6 m above the ground level and continue up to the tip of the tree at the interval of 2 m. We also measured the length of each section between two consecutive diameter measurement point and total height. We estimated breast height and absolute form factors, and calculated the arithmetic mean and variation of the form factors. We developed a model that can predict under bark diameter from over bark diameter and diameter at breast height (DBH) from stump diameter. Similarly, we developed models to predict stem volume using a different combination of predictor variables (DBH and/or height). The breast height form factor was 0.43 and absolute form factor was 0.40. The linear model fitted best to describe the under bark to over bark relation and DBH to stump diameter relation. Simple power function (R2=0.95) best fitted to our volume data. The product of squared DBH and height (R2=0.96) performed as the best predictor for volume prediction. Our form factor and volume model significantly differed with the previously developed form factor and models of Shorea robusta. Thus, we recommend developing site-specific form factors and volume models of Shorea robusta across the country. The models developed in this study are expected to contribute to predicting volume, biomass and carbon and thus contribute to sustainable forest management and may contribute to the calculation of the national carbon budget.