Data on structural characteristics from selected Polish and Bosnian primary forests

The data was collected in nine old-growth forests that have been under strict protection for at least 50 years. Three old-growth forests, i.e. Lom Reserve (BH-LM; N44.459326, E16.477032), Janj Reserve (BH-JA; N44.147635, E17.286488) and Perućica National Park (BH-PR; N43.29769, E18.724448), were located in the Dinaric Mountains in Bosnia and Herzegovina. The remaining stands were located in Poland, three of them were in the Carpathian Mountains, in the Beskid Sądecki. These were Baniska Reserve (PL-K1; N49.46064, E20.612551), Uhryn Reserve (PL-K2; N49.461494, E20.85624) and Hajnik Reserve (PL-K3; N49.331393, E20.95969). The three remaining stands were located within the Roztocze National Park and were stands number 227a (PL-R1; 50.5919, E23.0554), 285b (PL-R2; N50.5662, E23.0256) and 299a (PL-R3; N50.5559, E23.0280). In each stand, a 120 x 120 m research plot was set, where the diameters at breast height (DBH) and coordinates of all trees were measured. The plot was then divided into smaller spatial units to examine the fine-scale structural variability within stands. For plots 40 × 40 m (0.16 ha) the following stand structural variables were calculated: tree density per hectare (N), basal area per hectare (BA), Gini coefficient (GC), number of tree species (NS), and the number of 10 cm DBH classes (NDBH). The GC was computed with the following equation: GC = sum((2i -1- n)BA_i) / sum(BA_i(n - 1)), where i is the rank of the tree in ascending order of DBH, n is the total number of trees in a subplot and BA_i is the basal area (m²) of a tree with rank i.