A comparison of the urban flora of different phytoclimatic regions in Italy

This study is a comparison of the spontaneous vascular flora of five Italia n cities: Milan, Ancona, Rome, Cagliari and Palermo. The aims of the study are to test the hypothesis that urbanization results in uniformity of urban floras: and to evaluate the role of alien species in the flora of settleme nts located in different phytoclimatic regions. To obtain comparable data, ten plots of 1 ha, each representing typical urban habitats, were analysed in each city. The results indicate a low floristic similarity between the c ities, while the strongest similarity appears within each city and between each city and the seminatural vegetation of the surrounding region. In the Mediterranean settlements. even the most urbanized plots reflect the charac ters of the surrounding landscape and are rich in native species, while ali ens are relatively few. These results differ from the reported uniformity a nd the high proportion of aliens which generally characterize urban floras elsewhere. To explain this trend the importance of apophytes (indigenous pl ants expanding into man-made habitats) is highlighted; several Mediterranea n species adapted to disturbance (i.e. grazing, trampling, and human activi ties) are pre-adapted to the urban environment. In addition, consideration is given to the minor role played by the 'urban heat island' in the Mediter ranean basin, and to the structure and history of several Italian settlemen ts, where ancient walls, ruins and archaeological sites in the periphery as well as in the historical centres act as conservative habitats and provide connection with seed-sources on the outskirts.