Compatible tree volume and above-ground biomass equations for Chinese fir plantations in Guizhou

It has become a trend to supplement national forest resource monitoring with forest biomass estimation. Biomass equations to be developed should be compatible with volume equations. Based on the tree volume and above-ground biomass data of Chinese fir (Cunninghamia lanceolata) plantations of Guizhou Province in China, the compatible tree volume and above-ground biomass equations and biomass conversion functions were constructed using the error-in-variable modeling method. The results show that: 1) the regressions of volume equations improve significantly when tree height is used together with diameter at breast height (DBH), while the regressions of biomass equations improve slightly; 2) for biomass conversion function based on one variable, the conversion factor decreases with growing DBH; for conversion function based on two variables, the factor increases with rising DBH but decreases with growing tree height. Through the one variable-based compatible equations, the prediction precisions of tree volume and above-ground biomass estimates are more than 97% and 96% respectively; through the two variables-based equations, the prediction precision of tree volume estimates is more than 99%, but the precision of above-ground biomass estimates is only near 0.5 percentage higher than that through one-variable equation.