Abstract
This study reports the results of the evaluation of changes in the species diversity and composition of ruderal vegetation of three Slovak and one Czech city over the time. The dataset of 1489 relevés from five ruderal syntaxa from the cities Bratislava, Malacky, Trnava and Brno was used. Data were from two different time periods, the older dataset from the years 1960–1982, the more recent dataset from the years 2005–2016. The statistical analysis revealed the decrease of Shannon–Wiener diversity index of all (native + alien) species in the majority of classes of ruderal vegetation of cities. The analysis of the changes in the Pielou’s measure of species evenness showed that in some of the classes and cities, the species evenness remained unchanged, in the other ones it decreased. The percentage of native species in the ruderal vegetation did not change over the time, but the percentage of invasive alien species in the majority of syntaxa and cities increased significantly. In total, 38 invasive taxa were recorded in the ruderal vegetation of cities. Most of them are neophytes, therophytes and belong to the family Asteraceae. The majority of invasive taxa were recorded in both time periods. Some of the invasive species, e.g. Fallopia japonica and Juncus tenuis were recorded only in the more recent time period. Our results contribute to the knowledge about biological invasions in the cities.