Ninety years of alien plant species accumulation across regional and local scales in central European fields

Alien species are increasingly prevalent worldwide, leading to economic and biodiversity losses. We examined how the spread of non-crop alien plant species (i.e., archaeophytes and neophytes) has evolved in arable fields across ten countries in central Europe from 1930 to 2019. Specifically, we analyzed how regional and local trajectories of alien plant species have changed over the last ninety years. We used a dataset of 21,747 vegetation plots from the AgriWeedClim database and applied generalized linear mixed-effect models. We analyzed the percentage of plots containing neophytes to characterize regional scale dynamics, as well as the proportional number and relative abundance of alien species per plot, offering insights into the local scale dynamics of alien species spread in arable fields. The dynamics of species populations in the study area revealed significant contrasts between neophytes and archaeophytes over time. The percentage of plots containing neophytes strongly increased from 34.2 % in 1930 to 70.1 % in 2019. The proportion of neophytes, in plots nearly doubled from 5.5 % in 1930 to 10.2 % in 2019. The relative abundance, meaning their biomass relative to the total biomass of all species in the plot, of neophytes followed a similar upward trend increasing from 4.1 % to 9.9 %. This highlights not only the spatial spread of neophytes in arable vegetation but also their increasing cover on the local scale. Archaeophyte species displayed a different trajectory. Their proportion exhibited only a modest increase from 23.2 % to 25.3 % over the ninety-year period, while their relative abundance slightly decreased from 21.2 % to 19.5 %. A sensitivity analysis of our data further revealed that the temporal increase in the percentage of plots containing neophytes is mainly driven by a few common species, such as Veronica persica and Erigeron annuus, which had a high number of records during the study period. We anticipate an increasing occurrence of neophytes in local communities in the future, which may contribute to the homogenization of regional arable plant communities.