Sample tree data from the Swedish NFI used in Jacobsson, Jonas, Fridman, Jonas, Axelsson, Anna-Lena, Milberg, Per (2025). An aging population? A century of change among Swedish forest trees. Forest Ecology and Management. 580:122509. https://doi.org/10.1016/j.foreco.2025.122509 Contact: Jonas Fridman, riksskogstaxeringen@slu.se Column Description Year of Inventory Year of Inventory ClusterID Unique cluster ID PlotID Unique plot ID within cluster ID Landuse_code Landuse code (see below) Landuse_char Landuse classification in text (see below) Region Region used for analysis in publication: Norrbotten, South-central Sweden (SC Sweden), Rest of Sweden, see below. Within_formally_protected_areas0=No, 1= Yes. According to status 2023. Diameter (mm) Diameter at breast height (mm) Stem_volume (m3) Stem volume (m3) Age_breast_height Tree age at 1.3 m (yrs) Total_tree_age Total tree age (yrs) No_stems_exp_factor Expansion factor for the estimate of total number of stems (within period) Volume_m3_exp_factor Expansion factor for the estimate of total volume of stems (within period) Species_code Species code Species_latin Species name in latin Species_group Species group: Pine, Spruce, Deciduous Period 1926 (Inventory years 1923-1929), 1957 (1953-1962), 1987 (1983-1992), 2017 (2013-2022) Landuse_code Landuse_char 1 Productive forestland 4 Mire 6 Sub-alpine spruce forest 5 Rockland 3 Agricultural land 9 Other land 2 Agricultural land 14 Other land 10 Other land 8 Other land 20 Other land Region Description Norrbotten County of Norrbotten SC Sweden South-central Sweden. Include counties; Västra Götaland, Östergötland, Jönköping, Kalmar and Kronoberg Rest of Sweden All other Swedish counties