ABSTRACTThe carbon stored in small diameter trees of temperate forests has been ignored in most studies and there is a lack of biomass equations for this component of forests. We harvested nine main tree species at sapling stage (dbh < 8 cm) across different site conditions (from 100 to 1700 m a.s.l). For each species, 10–12 individuals were selected randomly and harvested. Using nonlinear seemingly unrelated regression (NSUR), additive species-independent equations were developed for estimation of biomass of foliage, branch, bole, and total based on dbh, height, and wood density as predictors. Results showed that wood density and height had high effects on equations performance except for the foliage equations. Comparing actual and estimated biomass for each species revealed that these equations can be used for new species in similar forests.