Species-specific basic density (BD) data are necessary to improve the indirect methods of biomass determination. The density of tree components (e.g., bark, branches, roots) is studied much less than that of stem wood. Nevertheless, ignoring the specific BD values of these components in biomass calculations can lead to errors. The study aims to investigate BD variation of aboveground and belowground tree components by studying a total of 162 gray alder (Alnus incana (L.) Moench) and common alder (Alnus glutinosa (L.) Gaertn.) trees. From them, 55 stumps were excavated to determine the BD of the belowground components. Our findings reveal that the volume-weighted BD of the stem (wood and bark) and the branch density of common alder are higher compared to gray alder. Both species have similar bark density, while the BD of belowground components is higher for gray alder. The stem wood density of both species increases upward from the stump to the top. Compared to gray alders, the stems of common alders have more distinct radial within-stem density variation. According to our results, the application of default Alnus spp. wood density values recommended in the IPCC guidelines for the calculation of total biomass and carbon stock is likely causing overestimation. The BD values obtained in our study on alders’ biomass components will allow for more accurate appraisals of total biomass and carbon stock for gray and common alder forests.

The ongoing shifts in natural vegetation zones predict the expansion of European beech (Fagus sylvatica L.) into the Eastern Baltic region, suggesting it will become a potential alternative to birch (Betula pendula Roth. and Betula pubescens Ehrh.) in forest regeneration. For a successful application of alternative forest regeneration material, an evaluation of susceptibility to natural disturbances (e.g., wind) is necessary for reliable projections of timber yield in the long term. This study compared the loading resistance of beech growing in the northeasternmost stands in Europe to local birch by applying the static tree-pulling test. Relationships between dimensions of aboveground parts and resistance against intrinsic wood damages (primary failure) and fatal (secondary) failure were similar between species. However, birch, which is more drought sensitive compared to beech, is suggested to have a higher susceptibility to post-storm legacy effects, supporting beech as a potential alternative to birch in terms of wind resistance.