Biodiversity changes in highly anthropogenic environments (cultivated and ruderal) since the Neolithic in eastern France

In highly anthropogenic plant communities, environmental conditions and human practices play a significant role in the composition, structure and diversity of the flora. This paper presents a study of current and past floras of two anthropogenic habitats (cultivated and ruderal) in eastern France that have been the subject of numerous palaeoenvironmental studies (pollen and seed analysis). To understand the different components that constitute the biodiversity of these floras, it is necessary to develop a transdisciplinary method combining ecology, phytogeography and palaeoenvironmental sciences. As a first step, a distinction has been made between native and alien plants as well as between two categories of the latter: archaeophytes (alien taxa introduced into a study area before AD 1500) and neophytes (alien taxa which became established after AD 1500). Second, the study of ecological characteristics of these species and the knowledge of human and climatic history of the region allow the elaboration of a synthesis of biodiversity evolution in these environments from the Neolithic to the present day. The results of this analysis show that there has been a constant enrichment of the anthropogenic flora by alien species through time. Two main periods can be emphasized: the first began in the late Neolithic and reached a peak in the late Bronze Age, the second began with the advent of Modern times. This kind of study has a double implication: first, by distinguishing between native and alien species (archaeophytes and neophytes) and by refining their ecological characteristics, the method allows a critical evaluation of the modern phytosociological units which are traditionally used to interpret fossil assemblages and to discriminate species that are ‘strong’ indicators of human activities. Second, the recognition of native and alien species also has implications for species invasion studies and for species conservation and vegetation management in anthropogenic habitats.