Determination of allometric equations for estimating stem biomass of three species of Pinus brutia Ten., Pinus pinea L. and Cupressus sempervirens L. in the Arabdagh reforests, Golestan province

Accurate measurements of above-ground biomass and selection of the most appropriate allometric equations are major challenges in evaluating tree biomass. Therefore, the development of allometric equations for each species is essential for accurate above-ground-biomass estimation. This study aimed to estimate the stem biomass of three conifers Pinus brutia, Pinus pinea, and Cupressus sempervirens in Arabdagh reforest using the allometric equations. In order to model the stem biomass, three main characteristics of diameter at breast height (DBH), height (H) and wood density (𝜌), were used separately and in combination to fit the equations. The results of this study showed that if the DBH alone was available for the Pinus brutia, the obtained equation had the highest coefficient of determination (R2) (0.90). By adding H and 𝜌 into DBH in stem allometric equation, the R2 increased by 9% and RMSE % decreased by 12.63%. For Pinus pinea, the results showed that if the DBH was available the obtained equation had the highest R2 (0.99). By adding H and 𝜌 into DBH in stem allometric equation, the R2 and RMSE % values did not improve. The results of Cupressus sempervirens, showed that if the DBH was available the obtained equation had the highest R2 (0.98) and the lowest RMSE% (9.81%). By adding H and 𝜌 into DBH in stem alometric equations, the R2 increased by 1% and RMSE% decreased by 3.59%. The results can be used to estimate the above-ground biomass with these species in similar climate and soil conditions at a local scale.