Belowground structure and allometric volume models of Norway spruce (Picea abies L. Karst) in Central European forests

: Understanding the structure and allocation of belowground biomass is essential for improving assessments of tree stability, biomass accumulation, and responses to environmental conditions. This study investigated biomass partitioning, root architecture, and allometric relationships of Norway spruce ( Picea abies L. Karst) using data from 100 trees sampled across ten sites in Central Europe, namely the Czech Republic and Slovakia. Stem and aboveground dimensions were measured, and root systems were excavated. The roots were then classified according to depth, and the volumes of stems, stumps, and roots were quantified. Allometric models based on tree height ( H ), diameter at 0.2 m ( D 0.2 ), and diameter at breast height ( D 1.3 ) were used to predict component volumes separately for stems, aboveground stumps, belowground stumps, and roots. Root distribution showed pronounced site-dependent variability. On average, 76.4% of root volume was concentrated within the upper 30 cm of soil, 16.7% occurred between 31 and 60 cm, and only 6.9% extended below 60 cm. Shallow rooting might be associated with waterlogged pseudogley soils and compact podzols. Stems represented the largest proportion of total volume of studied tree parts (77.9%), followed by roots (15.1%), belowground stumps (4.1%), and aboveground stumps (2.9%). Root contribution ranged from 10.4% to 24.0%. Allometric analyses demonstrated that D 1.3 was the most reliable predictor of tree component volumes, outperforming H and D 0.2 in most cases. Stem volume and total volume of studied tree parts were predicted with the highest accuracy, whereas belowground stump volume showed the greatest variability. These results highlight the importance of incorporating site-specific rooting characteristics into forest inventories and management practices, particularly in the context of increasing risks of drought and wind disturbance associated with climate change.