Abstract: To accurately estimate Masson pine forest biomass in China, we analyzed the estimation coefficients including the biomass conversion and expansion factor (BCEF), the biomass expansion factor (BEF), and the ratio of root to stem (R) with their influencing factors based on the data from related literature from 1982 to 2019. The results showed that the average values of BCEF, BEF and R were 0.723±0.138 t·m^-3, 1.390±0.184 and 0.167±0.024, respectively. BCEF, BEF and R all gradually decreased with increasing stand age (r²=0.329, 0.430 and 0.315, respectively) and stand stock volume (r²=0.513, 0.528 and 0.337, respectively), and gradually tended to be stable. BCEF, BEF and R all decreased first and then increased with increasing average tree height, with a fitting accuracy of 0.370, 0.506 and 0.239, respectively. BCEF decreased gradually with increasing average  diameter at breast height (r²=0.306). BEF decreased first and then increased with increasing average diameter at breast height (r²=0.531). There was no relationship between biomass estimation coefficients and climatic factors. R increased with slope (r²=0.298) and increased gradually with altitude (r²=0.277), while BCEF decreased first and then increased with altitude (r²=0.365). Natural pruning during the growth of Masson pine resulted in different stand structure. The slope and altitude would affect plant growth by affecting the availability of light, heat, and water. Hence, the stand structure and topographic factors had a higher degree of fitting with the biomass estimation coefficients. Therefore, the role of stand structure and topography should be considered when estimating the biomass of Masson pine by using biomass estimation coefficients.

Key words: Masson pine, biomass estimation coefficient, forest stand structure, climate, topography.