The importance of alien and native species in the urban flora of Rome (Italy)

The distribution and frequency of alien and native species in the flora of Rome (Italy) were compared and related to spatial variations within the study area [date not given]. Native species dominate throughout the city. Naturalized alien species tend to increase in riparian and most urbanized habitats; their relative proportion rises along with human impact, with urbanization and towards the centre of the city. The distribution pattern of those species confined to the inner city is due to the peculiar habitats found in the historical area, such as ancient walls and ruins, rather than to the warmer climate of the urban centre. This result bears out the hypothesis that one of the reasons for the relatively lesser presence of alien species in the flora of Mediterranean settlements, compared to Central European settlements, is the minor role played by the urban heat island in the immigration to the urban cores of species originating in warmer regions.