The Dutch databases FLORIVON en FlorBase are nation-wide databases which contain about 10 million records of occurrence of vascular plant species, collected in the 20th century on a scale of approximately 1 square km. In this study, these data are statistically analysed to find and identify relations between changes in botanical biodiversity and changes in climate and other environmental factors. Prior to the analysis, the data have been corrected for several major forms of survey bias. The records are grouped into three intervals covering the 20th century: 1902–1949, 1975–1984, and 1985–1999. For the intervals 1902–1949 and 1975–1984, we find small but significant increases in the presence of both ‘warm’ and ‘cold’ species. However, in the final decades of the 20th century we find a marked increase in ‘warm’ species only, coinciding with the marked increase in ambient temperature observed during this period. This is evidence for a rapid response of the Dutch flora to climatic change. Urbanisation is also examined as an alternative explanation for the increase in ‘warm’ plant species. It is found to explain only 50% of the increased presence of such species in the final decades of the 20th century. Besides temperature-related effects, the most important change during the 20th century was a strong decline in plant species of nutrient poor sites and a marked increase of plant species of nutrient rich sites.