Neo- and archaeophytes respond more strongly than natives to socio-economic mobility and disturbance patterns along an urban-rural gradient

To clarify the distribution and abundance of natives, archaeophytes and neophytes in settlements along an urban-rural gradient we investigated the importance of site-related and socio-economic factors within settlements in determining the abundance and species richness of these three groups of plant species. The Wetterau region north of Frankfurt/Main, Hesse, Germany. The occurrence and abundance of plant species were recorded in 2003 along transects in 66 settlements in a region north of Frankfurt/Main (Germany). The transect routes had been established in an earlier study in 1974-81. We used ordinations to analyse species composition, fitting 10 independent variables to explain the main gradient in species composition. Additionally, socio-economic styles (derived from interviews of 1359 households) were fitted, to analyse the influence of these on plant communities. Finally, we analysed species richness by calculating independent contributions of the variables using hierarchical partitioning. Many species of neophytes have expanded their range since the 1974-81 survey, but this was not associated with a general decline of archaeophytes and natives. The main variation of species composition was along a rural to urban gradient, associated with site conditions and with socio-economic factors that vary from settlements dominated by households rooted in the local community to settlements characterized by a mobile new middle class. For neophytes, variables describing the connection to Frankfurt (distance or connectivity) were most important in predicting species richness. For archaeophytes, the data showed a positive relationship between species richness and increasing herbicide application. These results suggest that the occurrence of neophytes within settlements along the urban-rural gradient is triggered by dispersal, related to human mobility patterns. In contrast, the occurrence of archaeophytes in settlements is determined by disturbance-related factors that predominantly depend on traditional gardening practices and weed control practices associated with farming.