Estimation of the biomass stock of trees in Sweden:: comparison of biomass equations and age-dependent biomass expansion factors

Differences and uncertainties of alternative methods applicable to estimation of biomass in national greenhouse gas inventories are evaluated. The alternative methods employed to obtain biomass estimates of trees are (1) aggregated stand-level volume estimates multiplied by biomass expansion factors (BEF), and (2) biomass equations applied to tree-wise data of a national forest inventory. In comparison to the reference value obtained using tree-wise biomass equations, the age-dependent BEFs for the whole of Sweden resulted in a 6.7% lower aboveground biomass estimate. The estimates were the closest for conifer-dominated forests in central Sweden, and the largest discrepancies were for spruce in southern Sweden. This result indicates that these age-dependent BEFs cannot be applied to conditions where stand development deviates from the conditions under which the BEFs were developed. The degree of uncertainty in both methods was highest in the young age-classes. At the regional level, the relative standard errors of the BEF-based biomass estimates were in the range of 4 - 13%.