Changes during the 20th century in species composition of synanthropic vegetation in Moravia (Czech Republic).

Variation in species composition and proportion of different plant traits were studied for weed and ruderal vegetation in the eastern part of the Czech Republic (Moravia), especially the temporal changes from the beginning of the 20th century up to 2005. Data sets for 433 weed species and 695 ruderal species were used in the analysis. While historical data on the occurrence of synanthropic species were obtained from floristic literature, that on recent occurrence were extracted from the Czech National Phytosociological Database. Species that were common in the past are still common a century later and rare species are becoming rarer. Almost a quarter of all synanthropic species recorded at the beginning of the last century are endangered species and 12 are now extinct in this country. Some trends in species composition and particular species attributes were found. While mean abundance of archaeophytes and native species decreased, mean abundance of neophytes increased in both vegetation types during the last century. The use of regression tree models revealed that the relative abundance of weed and ruderal species is related to their species attributes, i.e. Ellenberg indicator value, lifespan, life strategy, pollination mode, plant height and flowering period. The most abundant weed species have always been shade-tolerant, relatively small plants that are able to flower for a long time and require high levels of nutrients. The most abundant weed species changed from insect-pollinated to those without any specific pollination mode. A long flowering period is an important attribute of the most abundant ruderal species. There was no significant change in ecological preferences of ruderal species. Regarding the life strategy of these species, CR-strategists were the most abundant in 1908 but less common in 2005 and partly replaced by C-strategists.