Diversity of flora and vegetation in European cities as a potential for nature conservation in urban-industrial areas - with examples from Berlin and Potsdam (Germany)

Cities and urban-industrial conglomerations are continuously gaining importance as living spaces for humans. Sustainable urban development as well as nature conservation in cities are and will be the major tasks of the people living in densely populated areas. Cities have to be regarded as a new type of environment with species compositions and habitats peculiar to urban-industrial areas. This new type of environment can be highly diverse on the species and habitat level. Reasons for this are (1) the heterogeneity of settlement and land use patterns in cities, (2) the introduction and dispersal of non-native species directly or indirectly through transport and traffic, (3) the evolution of new taxa (speciation) on man-made sites within and outside settle- ments and (4) the floristic richness of a given surrounding geographical area. Selected habitats in Berlin and Potsdam (NE-Germany) have been investigated with a focus on diversity of flora, vegetation and land use patterns. The correlation between the number of plant species and the diversity of land use patterns is shown with a transect from the centre to the outskirts of Berlin. In residential areas built in the 1920s and 1930s, the flora is studied from a historical and current perspective to assess their diversity of wild-growing indigenous and non- native plant species, wild-growing ornamental plant species and planted trees. Historical land- scape gardens in Potsdam show a characteristic composition in flora and vegetation (e. g. meadows and lawns) very different from all other land use types in the city and its surroundings due to their historical garden design and the existence of semi-natural habitats. Biological diversity in cities should be recognized as an opportunity for nature conservation and a challenge for sustainable development of urban-industrial areas. Main principles of nature conservation in cities are discussed, which are closely related to the maintenance and development of biological diversity in cities, aiming at habitat as well as species diversity. These are (1) historical continuity, (2) urban ecological zonation on a small scale (city), (3) maintenance of land use diversity on a large scale (city districts, residential areas etc.), and (4) maintenance of local variety.