Data on farmland plants consist of distribution grid data per 1 km2 grid, aggregated into 20-25 year periods. Hardly any data were collected between 1950 and 1975; hence, this period was left out of the analysis. Trends in distribution (the number of occupied 1 km2 grids) are considered an approximation of the trend in population numbers. The selection of species has been derived from an often used classification in ecological plant groups by Arnolds & Van der Maarel (1979).
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