Data from: More is less: net gain in species richness, but biotic homogenization over 140 years

While biodiversity loss continues globally, assessments of regional and
local change over time have been equivocal. Here, we assess changes in
plant species richness and beta diversity over 140 years at the level of
regions within a country. Using 19th‐century flora censuses for 14 Danish
regions as a baseline, we overcome previous criticisms concerning short
time series and neglect of completely altered habitats. We find that
species composition has changed dramatically and directionally across all
regions. Substantial species losses were more than offset by large gains,
resulting in a net increase in species richness in all regions. The
occupancy of initially widespread species increased, while initially rare
species lost terrain. These changes were accompanied by strong biotic
homogenization; i.e. regions are more similar now than they were 140 years
ago. Species declining in Denmark were found to be in similar decline all
over Northern Europe.