Ancient and Early Medieval man-made habitats in the Czech Republic: colonization history and vegetation changes

The invasion history of archaeophytes (i.e. alien taxa that were introduced into Europe prior to AD 1500), their effect on past vegetation and their present status based on their residence time were studied. The residence times of archaeophytes range from 7500 to 500 years. It is likely that species with other functional traits came at different times. We summarized assemblages of macroremains obtained from the Archaeobotanical Database of the Czech Republic. The data based on 202 archaeological sites cover the period from the Neolithic to the Early Middle Ages. We found 123 alien species and 94 synanthropic species native in the Czech Republic. Three waves of immigration of increasing magnitude were distinguished: (i) the Neolithic, (ii) the Bronze Age, and (iii) the Early Middle Ages. The first phase of synanthropic plant immigration was characterized by the prevalence of native and alien generalist species, which are still very abundant, sharing both ruderal and segetal habitats. Specialist weeds of cereal fields occurred only since the Eneolithic. In the ruderal flora, the successive development started from a stage dominated by species associated with disturbance of less fertile soils and species that need nutrient-rich soils prevailed later. The composition of the oldest grassland flora corresponded with that of short lawns at disturbed and/or trampled sites, whereas a sudden increase in meadow species occurred in the Late Bronze Age. Since the Middle Ages, pastural species, avoided by grazing animals, indicate the intense use of pastures and their expansion into wet conditions. The species that arrived early in this era, i.e. in the Neolithic, are currently more successful than the later arrivals. Such a trend cannot be explained by the length of time they have had to naturalize and spread because all archaeophytes have been here long enough, whether they arrived early or late, to be fully naturalized. The success of the abundant and invasive species is not due to their long residence times; on the contrary, they arrived early due to their invasiveness, which is a result of their biological traits. A contrasting strategy is that of the specialized weeds of cereal fields. Unlike ruderal species, they rarely spread from cultivated land. Therefore, many of these ecological specialists remained common until the early 20th century, but then modern agriculture practices resulted in a great reduction in their abundance.