Habitat specialists and generalists drive homogenization and differentiation of temperate forest plant communities at the regional scale

After two decades, the forest communities did not yet exhibit severe biotic impoverishment, although there was a broad trend towards homogenization. The actual magnitude of change depended on which beta diversity measure was applied. The downward trend was primarily the result of the spread of native species that are able to tolerate broad pH and moisture ranges. A distinction between forest specialists (closely tied to forest habitats) and generalists (also found in open habitats) did not help explain changes in beta diversity. The study shows that on the regional scale and in habitats not yet threatened by the invasion of alien species, shifts in native species can promote biotic homogenization.