•We analyzed chronosequences of Picea abies and Fagus sylvatica stands.•We found small differences in biomass allocation, production and carbon content.•This increases the transferability of models used in carbon inventories.•We provided tree- and stand-level models for biomass and carbon mass estimates. Despite different levels of complexity among biomass models, it is unclear how much patterns of biomass production and allocation differ between mountain and lowland forests, and how much neglecting this difference biases carbon pool estimations. To address this question, we studied chronosequences of 24 Fagus sylvatica and 24 Picea abies stands in Poland, located both in lowlands and highlands (12 stands of each species per category). We cut and weighted 192 sample trees, and we measured carbon content in wood, bark, branches and leaves. We also developed allometric tree- and stand-level models of biomass and carbon mass. Using log-transformed linear models we checked the effect sizes of elevation category (lowland and highland) on estimate output. We found small, statistically insignificant differences in biomass allocation patterns, carbon content and allometric trajectories in trees between lowland and highland stands. Tree-level allometric models without elevation category had higher accuracy than models including elevation category and explained 96.8–99.8% of biomass variability. Biomass and carbon stock of species studied was positively correlated with stand volume, age, basal area and height, and negatively with stand density. However, the differences between lowlands and highlands were low and did not exceed 38 Mg ha−1 (for P. abies foliage biomass, with model root mean squared error of 37.638 Mg ha−1). Our results revealed transferability of models developed using lowland and highland populations of the studied species. This will increase confidence in methods used to estimate carbon pools.