10.18710/VYQFPKMaliniemi, TuijaTuijaMaliniemi0000-0003-1218-6554University of OuluKiilunen, PetteriPetteriKiilunen0000-0002-1326-2291University of OuluBråthen, Kari AnneKari AnneBråthen0000-0003-0942-1074UiT The Arctic University of NorwayKapfer, JuttaJuttaKapfer0000-0002-8077-8917Norwegian Institute of Bioeconomy ResearchBockelie Rosendal, TorunnTorunnBockelie RosendalUiT The Arctic University of NorwayGrytnes, John-ArvidJohn-ArvidGrytnes0000-0002-6365-9676Norwegian University of Life SciencesSaccone, PatrickPatrickSaccone0000-0001-8820-593XInstitute of Botany of the Czech Academy of SciencesVirtanen, RistoRistoVirtanen0000-0002-8295-8217University of OuluDataverseNO2025Earth and Environmental Sciencesbiodiversity changevegetation resurveyheathlandstundraEmpetrum nigrumcrowberrybiotic homogenisationMaliniemi, TuijaTuijaMaliniemiUniversity of OuluBråthen, Kari AnneKari AnneBråthenUiT The Arctic University of NorwayUniversity of OuluUiT The Arctic University of NorwayTuija MaliniemiTuijaMaliniemiTuija MaliniemiTuijaMaliniemiPetteri KiilunenPetteriKiilunenKari Anne BråthenKari AnneBråthenJutta KapferJuttaKapferTorunn Bockelie RosendalTorunnBockelie RosendalRisto VirtanenRistoVirtanenUiT The Arctic University of Norway2025-08-012025-10-131964/19752013/2023survey data10.1002/ecog.0792110626436509139229764328105text/plaintext/comma-separated-valuestext/comma-separated-valuestext/comma-separated-valuestype/x-r-syntax1.1CC0 1.0This dataset contain plant community data (including vascular plants, bryophytes and lichens) from 275 vegetation plots from northern Fennoscandia (northern Finland and northern Norway). Values for each species are percentage cover estimates from 2 x 2 meter plot. Each plot has been surveyed twice, i.e., species have old and new percentage cover from 1964-75 and from 2013-23. We analyzed temporal changes in community composition and diversity across the study area and in different biogeographic zones, continentality-humidity classes and habitat types. We found a strong homogenization trend across the study area, with plant communities becoming more similar in composition over the decades when all taxa were treated together. The observed homogenization was driven especially by the increased similarity of vascular plant and lichen communities and was largely independent of biogeographic zones or continentality-humidity gradient. Homogenization was particularly associated with the drastic encroachment of the evergreen dwarf shrub Empetrum nigrum in habitat types originally dominated by other species, and with the decrease in lichen cover. In general, our findings suggest that Fennoscandian heathland and tundra vegetation is transforming towards a more homogeneous evergreen dwarf shrub-dominated system, which may threaten ecosystem multifunctionality. Our results highlight the importance of exploring biodiversity among different metrics and growth forms to understand the overall changes in heathland and tundra biodiversity.R statistical environment, 4.4.131661771Research Council of Finland259072Norwegian Research Council302749Foundations Post Doc poolFinnish Cultural FoundationResearch Council of FinlandProfi6, 336449, Biodiverse AnthropocenesKvantum InstituteUniversity of OuluINTERACT262693, 730938